drm/panel: Augment the TPO TPG110 bindings

The TPO TPG110 bindings were using the DPI bindings (popular
in the fbdev subsystem) but this misses the finer points
learned in the DRM subsystem.

We need to augment the bindings for proper DRM integration:
the timings are expressed by the hardware, not put into the
device tree. I.e. this hardware is self-describing and can
report the resolutions and timings needed. It should not
be described in the device tree.

Further the device was incorrectly modeled with GPIO lines
instead of an SPI child, even though the device was using
SPI.

No known deployments of the device using device tree
exist, so it should be fine to augment the bindings.

Cc: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20181101213256.12097-1-linus.walleij@linaro.org