mmc: sdhci: Add support for HOST_CONTROL2 and setting UHS timings

The HOST_CONTROL2 register is a part of SDHC v3.00 and not just specific
to arasan/zynq controllers. Add the same to sdhci.h.

Also create a common API to set UHS timings in HOST_CONTROL2.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>