arm: da850: configure LCDC fifo threshold

Configure fifo threshold in raster dma_control register to
512 bytes. This reduces LCDC underflow errors.

Signed-off-by: Manjunathappa, Prakash <prakash.pm@ti.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>