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>