video: Add support for SSD2828 (parallel LCD to MIPI bridge)

SSD2828 can take pixel data coming from a parallel LCD interface
and translate it on the fly into MIPI DSI interface for driving
a MIPI compatible TFT display. SSD2828 is configured over SPI
interface, which may or may not have MISO pin wired up on some
hardware. So a write-only SPI mode also has to be supported.

The SSD2828 support code is implemented as a utility function
and needs to be called from real display drivers, which are
responsible for driving parallel LCD hardware in front of the
video pipeline. The usage instructions are provided as comments
in the header file.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Anatolij Gustschin <agust@denx.de>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>