da8xx-fb: cleanup LCDC configurations

Configure below LCDC configurations to optimal values, also have an
option configure these optional parameters for platform.
1) AC bias configuration: Required only for passive panels
2) Dma_burst_size:
3) FIFO_DMA_DELAY:
4) FIFO threshold: Does not apply for da830 LCDC.

Patch is verified for 16bpp and 24bpp configurations on da830, da850 and
am335x EVMs.

Signed-off-by: Manjunathappa, Prakash <prakash.pm@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>