HID: plantronics: Update to map volume up/down controls

Update Kconfig with enhanced help text for hid-plantronics driver.

Update hid-plantronics.c to identify device type and correctly map
either the vendor unique or consumer control volume up/down usages
to KEY_VOLUMEUP and KEY_VOLUMEDOWN events. Unmapped usages are ignored
to prevent core mapping of unknown usages to random mouse events.

Tested on ChromeBox/ChromeBook with various Plantronics devices.

Signed-off-by: Terry Junge <terry.junge@plantronics.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
index 15338af..cc4c664 100644
--- a/drivers/hid/Kconfig
+++ b/drivers/hid/Kconfig
@@ -634,7 +634,12 @@
 	tristate "Plantronics USB HID Driver"
 	depends on HID
 	---help---
-	Provides HID support for Plantronics telephony devices.
+	  Provides HID support for Plantronics USB audio devices.
+	  Correctly maps vendor unique volume up/down HID usages to
+	  KEY_VOLUMEUP and KEY_VOLUMEDOWN events and prevents core mapping
+	  of other vendor unique HID usages to random mouse events.
+
+	  Say M here if you may ever plug in a Plantronics USB audio device.
 
 config HID_PRIMAX
 	tristate "Primax non-fully HID-compliant devices"