Older kernel versions or systems which do not connect eMMC reset line
properly may not be able to handle situations where either the eMMC
is left in HS200/HS400 mode or SD card in UHS modes by the bootloader
and may misbehave. Downgrade the eMMC to HS/HS52 mode and/or SD card
to non-UHS mode before booting the kernel to allow such older kernels
to work with modern U-Boot.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Tom Rini <trini@konsulko.com>