drm/panel: Add driver for sitronix ST7789V LCD controller

The Sitronix ST7789v controller is used to drive 240x320 LCD panels through
various interfaces, including SPI and RGB/Parallel.

The current driver is configuring it for the latter. Support for tinyDRM
can always be added later.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>