The NanoPi R4S leaves the SD card in 1.8V signalling when rebooting
while U-Boot requires the card to be in 3.3V mode.
Remove UHS support from the SD controller so the card remains in 3.3V
mode. This reduces transfer speeds but ensures a reboot whether from
userspace or following a kernel panic is always working.
Signed-off-by: David Bauer <mail@david-bauer.net>
