The A80 Optimus board exposes uart4 on the GPIO expansion header.
Enable it so we can use it.

Also enable the internal pull-ups, as there doesn't seem to be
external pull-up resistors for pins on the expansion header.
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>