HID: hid debug from hid-debug.h to hid layer

hid-debug.h contains a lot of code, and should not therefore
be a header.

This patch moves the code to generic hid layer as .c source, and
introduces CONFIG_HID_DEBUG to conditionally compile it, instead
of playing with #define DEBUG and including hid-debug.h.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/usb/input/hid-core.c b/drivers/usb/input/hid-core.c
index 1fa42f4..6938c4e 100644
--- a/drivers/usb/input/hid-core.c
+++ b/drivers/usb/input/hid-core.c
@@ -35,6 +35,7 @@
 
 #include <linux/hid.h>
 #include <linux/hiddev.h>
+#include <linux/hid-debug.h>
 #include "usbhid.h"
 
 /*