arm64: dts: allwinner: a100: set maximum MMC frequency

arm64: dts: allwinner: a100: set maximum MMC frequency

The manual for the Allwinner A133 SoC mentions that the maximum
supported MMC frequency is 150 MHz, for all of the MMC devices.

Describe that in the DT entry, to help drivers setting the right
interface frequency.

Fixes: fcfbb8d9ec58 ("arm64: allwinner: a100: Add MMC related nodes")
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Link: https://patch.msgid.link/20250505202416.23753-1-andre.przywara@arm.com
Signed-off-by: Chen-Yu Tsai <wens@csie.org>