dt-bindings: display: Add support for PDA 91-00156-A0 panel

PDA 91-00156-A0 5.0 is a 5.0" WVGA TFT LCD panel. This panel with
backlight is found in PDA 5" LCD screen (TM5000 series or AC320005-5).
Adding device tree bindings for this panel.

Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
[eugen.hristev@microchip.com]: specified backlight and supply bindings
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1547458584-29548-3-git-send-email-eugen.hristev@microchip.com