V4L/DVB: V4L: Events: Add documentation

Add documentation on how to use V4L2 events, both for V4L2 drivers and for
V4L2 applications.

Signed-off-by: Sakari Ailus <sakari.ailus@maxwell.research.nokia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/Documentation/DocBook/media-entities.tmpl b/Documentation/DocBook/media-entities.tmpl
index c725cb8..770be3c 100644
--- a/Documentation/DocBook/media-entities.tmpl
+++ b/Documentation/DocBook/media-entities.tmpl
@@ -17,6 +17,7 @@
 <!ENTITY VIDIOC-DBG-G-REGISTER "<link linkend='vidioc-dbg-g-register'><constant>VIDIOC_DBG_G_REGISTER</constant></link>">
 <!ENTITY VIDIOC-DBG-S-REGISTER "<link linkend='vidioc-dbg-g-register'><constant>VIDIOC_DBG_S_REGISTER</constant></link>">
 <!ENTITY VIDIOC-DQBUF "<link linkend='vidioc-qbuf'><constant>VIDIOC_DQBUF</constant></link>">
+<!ENTITY VIDIOC-DQEVENT "<link linkend='vidioc-dqevent'><constant>VIDIOC_DQEVENT</constant></link>">
 <!ENTITY VIDIOC-ENCODER-CMD "<link linkend='vidioc-encoder-cmd'><constant>VIDIOC_ENCODER_CMD</constant></link>">
 <!ENTITY VIDIOC-ENUMAUDIO "<link linkend='vidioc-enumaudio'><constant>VIDIOC_ENUMAUDIO</constant></link>">
 <!ENTITY VIDIOC-ENUMAUDOUT "<link linkend='vidioc-enumaudioout'><constant>VIDIOC_ENUMAUDOUT</constant></link>">
@@ -60,6 +61,7 @@
 <!ENTITY VIDIOC-REQBUFS "<link linkend='vidioc-reqbufs'><constant>VIDIOC_REQBUFS</constant></link>">
 <!ENTITY VIDIOC-STREAMOFF "<link linkend='vidioc-streamon'><constant>VIDIOC_STREAMOFF</constant></link>">
 <!ENTITY VIDIOC-STREAMON "<link linkend='vidioc-streamon'><constant>VIDIOC_STREAMON</constant></link>">
+<!ENTITY VIDIOC-SUBSCRIBE-EVENT "<link linkend='vidioc-subscribe-event'><constant>VIDIOC_SUBSCRIBE_EVENT</constant></link>">
 <!ENTITY VIDIOC-S-AUDIO "<link linkend='vidioc-g-audio'><constant>VIDIOC_S_AUDIO</constant></link>">
 <!ENTITY VIDIOC-S-AUDOUT "<link linkend='vidioc-g-audioout'><constant>VIDIOC_S_AUDOUT</constant></link>">
 <!ENTITY VIDIOC-S-CROP "<link linkend='vidioc-g-crop'><constant>VIDIOC_S_CROP</constant></link>">
@@ -141,6 +143,8 @@
 <!ENTITY v4l2-enc-idx "struct&nbsp;<link linkend='v4l2-enc-idx'>v4l2_enc_idx</link>">
 <!ENTITY v4l2-enc-idx-entry "struct&nbsp;<link linkend='v4l2-enc-idx-entry'>v4l2_enc_idx_entry</link>">
 <!ENTITY v4l2-encoder-cmd "struct&nbsp;<link linkend='v4l2-encoder-cmd'>v4l2_encoder_cmd</link>">
+<!ENTITY v4l2-event "struct&nbsp;<link linkend='v4l2-event'>v4l2_event</link>">
+<!ENTITY v4l2-event-subscription "struct&nbsp;<link linkend='v4l2-event-subscription'>v4l2_event_subscription</link>">
 <!ENTITY v4l2-ext-control "struct&nbsp;<link linkend='v4l2-ext-control'>v4l2_ext_control</link>">
 <!ENTITY v4l2-ext-controls "struct&nbsp;<link linkend='v4l2-ext-controls'>v4l2_ext_controls</link>">
 <!ENTITY v4l2-fmtdesc "struct&nbsp;<link linkend='v4l2-fmtdesc'>v4l2_fmtdesc</link>">
@@ -200,6 +204,7 @@
 <!ENTITY sub-controls SYSTEM "v4l/controls.xml">
 <!ENTITY sub-dev-capture SYSTEM "v4l/dev-capture.xml">
 <!ENTITY sub-dev-codec SYSTEM "v4l/dev-codec.xml">
+<!ENTITY sub-dev-event SYSTEM "v4l/dev-event.xml">
 <!ENTITY sub-dev-effect SYSTEM "v4l/dev-effect.xml">
 <!ENTITY sub-dev-osd SYSTEM "v4l/dev-osd.xml">
 <!ENTITY sub-dev-output SYSTEM "v4l/dev-output.xml">
@@ -292,6 +297,8 @@
 <!ENTITY sub-v4l2grab-c SYSTEM "v4l/v4l2grab.c.xml">
 <!ENTITY sub-videodev2-h SYSTEM "v4l/videodev2.h.xml">
 <!ENTITY sub-v4l2 SYSTEM "v4l/v4l2.xml">
+<!ENTITY sub-dqevent SYSTEM "v4l/vidioc-dqevent.xml">
+<!ENTITY sub-subscribe-event SYSTEM "v4l/vidioc-subscribe-event.xml">
 <!ENTITY sub-intro SYSTEM "dvb/intro.xml">
 <!ENTITY sub-frontend SYSTEM "dvb/frontend.xml">
 <!ENTITY sub-dvbproperty SYSTEM "dvb/dvbproperty.xml">
@@ -381,3 +388,5 @@
 <!ENTITY reqbufs SYSTEM "v4l/vidioc-reqbufs.xml">
 <!ENTITY s-hw-freq-seek SYSTEM "v4l/vidioc-s-hw-freq-seek.xml">
 <!ENTITY streamon SYSTEM "v4l/vidioc-streamon.xml">
+<!ENTITY dqevent SYSTEM "v4l/vidioc-dqevent.xml">
+<!ENTITY subscribe_event SYSTEM "v4l/vidioc-subscribe-event.xml">