Backport nwl+mxsfb+rocktech panel to 5.3

This backports the nwl and mxsfb drivers from linux-next to 5.3.

I did not adjust the DT for the phone (hence wip) since i have no means of testing birch but i'll look into fixing this for aspen.

Note that this needs mesa 19.2 since 18.x lacks mxsfb support. Display blank/unblank was tested with the corresponding compositor fixes.

Closes: https://source.puri.sm/Librem5/use-cases/issues/157 https://source.puri.sm/Librem5/use-cases/issues/140 https://source.puri.sm/Librem5/linux-next/issues/77