HID: Add input_register callback.

Add input_register callback which gets called after
hid_configure_usage is called for all the reports
and before the input device is registered. This allows
individual drivers to do extra work like input mapping just
before device registration.

Based on discussions with David Herrmann <dh.herrmann@googlemail.com>

Change-Id: Idab6fb4f7b1e5e569bd0410967288717e9d34c98
Signed-off-by: Jaikumar Ganesh <jaikumarg@android.com>

Changed to add return code to input_configured instead of
adding input_register

Signed-off-by: Arve Hjønnevåg <arve@android.com>