The lcd driver now works but is awfully slow. The trick is to put it in system
mode instead of RGB and setup 16bpp. The GRAM data can then be sent directly
with the SPI but since it's bit-banged and the CPU running at slow speed,
full screen refresh takes over a second, even with a slightly optmised version.
The OF uses a DMA mechanism with a proper LCD controller but the setup is much
more complicated and doesn't work at the moment.
Change-Id: I6c95d91de31bff97d0a5848b8e2078c21deb5895
