ARM: dts: dra7: Add "max-frequency" property to MMC dt nodes

Add "max-frequency" property to MMC dt nodes and set the
maximum frequency to 192MHz for MMC1/MMC2, 64MHz for MMC3
and 192MHz for MMC4. pdata quirks must be utilized to
detect presence of rev 1.1/1.0 of silicon and adjust
maximum frequencies as per restrictions documented in i843.

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