ARM: dts: dra7: Add high speed modes capability to MMC1/MMC2 dt node

While the supported UHS mode can be obtained from CAPA2
register, SD Host Controller Standard Specification
doesn't define bits for MMC's HS200 and DDR mode capability.
Add properties to indicate MMC HS200 and DDR speed mode capability in
dt node.

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