staging: fbtft: add support for ST7789V display controller

This patch adds support for the Sitronix ST7789V display controller.
The controller is intended for small color displays with a resolution
of up to 320x240 pixels.

Signed-off-by: Dennis Menschel <menschel-d@posteo.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>