drm/panel: simple: Add URT UMSH-8596MD-xT panels support

Add support for United Radiant Technology UMSH-8596MD-xT 7.0" WVGA TFT
LCD panels in the simple-panel driver.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Thierry Reding <treding@nvidia.com>