ARM: dts: suniv: F1C100: add MMC controllers

The F1C100 series contains two MMC controllers, where the first one is
typically connected to an (micro)SD card slot (as this is the one the
BROM is able to boot from).
Describe the two controllers in the SoC .dtsi.
We also add the pinctrl description for MMC0, since this is the only
pin set supporting that function anyway, and SD cards are very common
across boards.

Signed-off-by: Jesse Taube <Mr.Bossman075@gmail.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20220317162349.739636-9-andre.przywara@arm.com