lcd: Add CONFIG_LCD_ALIGNMENT to select frame buffer alignment

The normal alignment is PAGE_SIZE, but if this is defined, we can support
other alignments.

The motivation for this change is to make the display section-aligned on
ARM so that we can easily turn off data caching for the frame buffer region
without resorting to level 2 page tables.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>