mmc: sdhci-esdhc-imx: add ADMA Length Mismatch errata fix

The uSDHC has an ADMA Length Mismatch errata ERR004536 which may
cause ADMA work abnormally. The errata has already been fixed for
i.MX6Q TO1.2 and i.MX6DL TO1.1 by enable the bit 7 in 0x6c register.
Unfortunately this fix is not included in i.MX6SL.
So we disable ADMA for i.MX6SL and use SDMA instead.

Signed-off-by: Dong Aisheng <aisheng.dong@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>