HID: input: map digitizer battery usage

HID: input: map digitizer battery usage

We already mapped battery strength reports from the generic device
control page, but we did not update capacity from input reports, nor we
mapped the battery strength report from the digitizer page, so let's
implement this now.

Batteries driven by the input reports will now start in "unknown" state,
and will get updated once we receive first report containing battery
strength from the device.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>