Add's support to Raspberry Pi's 7" Touch device. Instead of using a
conventional bus all information is copied into a memory mapped area by
RPi's firmware.

Based on the driver found in RPi's kernel repository.
Signed-off-by: NNicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: NRob Herring <robh@kernel.org>
Acked-by: NEric Anholt <eric@anholt.net>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>