mmc: sdhci: Enable high speed conditional on the corresponding bit

The capabilities register has a field to indicate whether the host
supports high speed mode or not. Add high speed host_caps based on
this bit instead of enabling it by default.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Reviewed-by: Michal Simek <michal.simek@xilnx.com>
Tested-by: Michal Simek <michal.simek@xilnx.com>
(zcu104 with sdhci-caps-mask = <0 0x200000>;)