mmc: Imply HS200 cap with mmc-hs400 prop to match linux

eMMC nodes in linux device tree files typically only contain a mmc-hs400
prop to signal support for both HS400 and HS200. However, U-Boot require
an explicit mmc-hs200 prop to signal support for the HS200 mode.

Fix this by follow linux and imply HS200 cap when HS400 cap is signaled
using a mmc-hs400 prop.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Reviewed-by: Quentin Schulz <quentin.schulz@theobrma-systems.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>