arm64: allwinner: h6: enable MMC0/2 on Pine H64

The Pine H64 board have a MicroSD slot connected to MMC0 controller of
the H6 SoC and a eMMC slot connected to MMC2.

Enable them in the device tree.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>