mmc: sdhci-esdhc-imx: add preset value quirk for mx6

The i.MX6 does not support preset value feature.

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