drm/panel: Add Ilitek ILI9322 driver

This adds support for the Ilitek ILI9322 QVGA (320x240)
TFT panel driver.

This panel driver supports serial or parallel RGB or
YUV input and also ITU-T BT.656 input streams.

The controller is combined with a physical panel and
configured through the device tree.

Cc: David Lechner <david@lechnology.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Ben Dooks <ben.dooks@codethink.co.uk>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20171221234411.12156-1-linus.walleij@linaro.org