configs: dra7xx_evm: Enable support for the HS200 mmc mode in the SPL

Beside enabling the support for HS200 in mmc core, enabling the HS200
support in the SPL requires multi-dtb support in the SPL because pinctrl
and IOdelays vary across SOCs.

Also we need to make sure that the pinctrl properties arenot removed from
the dts by setting CONFIG_OF_SPL_REMOVE_PROPS to remove only clocks and
interrupts properties.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>