ARM: dts: dra72-evm: Set max clock frequency of MMC1 and MMC2

MMC1 supports SDR104 and MMC2 supports HS200 both of which requires
192MHz clock. Set the maximum operating clock frequency to 192 MHz.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>