HID: add KEY_CAMERA_FOCUS event in HID

Our HID device need KEY_CAMERA_FOCUS event to control camera,
but this event is non-existent in current HID driver.
So we add this event in hid-input.c.

Signed-off-by: fengqi <fengqi@xiaomi.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>