Input: qt1050 - add Microchip AT42QT1050 support

Add initial support for the AT42QT1050 (QT1050) device. The device
supports up to five input keys, dependent on the mode. Since it adds only
the initial support, the "1 to 4 keys plus Guard Channel" mode isn't
supported.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>