lcd: dt: extract simplefb support

We now have api functions that can support compiling simplefb code as its own
module. Since this code is not part of the display functionality, extract it
to its own file.

Raspberry Pi is updated to accommodate the changes.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Bo Shen <voice.shen@atmel.com>
Tested-by: Josh Wu <josh.wu@atmel.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Stephen Warren <swarren@wwwdotorg.org>