video: fbdev: mmp: add COMPILE_TEST support

Add COMPILE_TEST support to mmp display subsystem for better compile
testing coverage.

Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d21a19ea-8c18-80df-ae79-76de7c5ee67c@samsung.com