drm/panel: simple: Add Tianma TM070RVHG71 panel support

The Tianma TM070RVHG71 is a 7" WVGA (800x480) TFT LCD panel connected
via LVDS and can be supported by the simple-panel binding.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171107153058.5554-1-lukma@denx.de