drm/bridge: tc358762: Guess the meaning of LCDCTRL bits

The register content and behavior is very similar to TC358764 VP_CTRL.
All the bits except for unknown bit 6 also seem to match, even though
the datasheet is just not available. Add a comment and reuse the bit
definitions.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230615201902.566182-4-marex@denx.de