Input: adbhid - capslock and power button fix

If the adbhid module parameter restore_capslock_events is used,
pressing the power button may confuse the capslock state. This is
because the power button release scancode (0xff) is sometimes the same
as the capslock press/release scancode.

This fix adds yet another flag to track the state of the power button
so that it works independently of capslock.

Signed-off-by: Rodney Lorrimar <rodney@rodney.id.au>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>