The A64 has 3 MMC controllers, one of them being especially targeted to
eMMC. Among other things, it has a data strobe signal and a 8 bits data
width.

The two other are more usual controllers that will have a 4 bits width at
most and no data strobe signal, which limits it to more usual SD or MMC
peripherals.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Tested-by: Florian Vaussard <florian.vaussard@heig-vd.ch>
Acked-by: Chen-Yu Tsai <wens@csie.org>