drm/msm/mdp4: add lcdc-align-lsb flag to control lane alignment

This allows controlling which of the 8 lanes are used for 6 bit color.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>