staging: fbtft: Add support for Himax HX8357D controller

The Himax HX8357D is used e.g. by the Adafruit PITFT Plus 3.5".
Adafruit added HX8357D support to an own fork of fbtft and support
Raspbian only (https://github.com/adafruit/adafruit-rpi-fbtft/).
They don't intend to push it upstream but gave me the ok to do so.
Original author: Sean Cross <xobs@kosagi.com>

I just applied small changes to the driver to align it with the other
fbtft drivers.
- add "compatible" argument to FBTFT_REGISTER_DRIVER call
- add missing MODULE_ALIAS declarations

Tested successfully with this display on an RPI2 under Arch Linux ARM
(kernel 3.18.13).

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>