mmc: sdhci-esdhc-imx: add eMMC HS200 mode support

Add support for eMMC 4.5 cards to work on hs200 mode.

Signed-off-by: Dong Aisheng <b29396@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>