mmc: sdhci-esdhc-imx: set the correct max timeout value for uSDHC

The default sdhci driver write 0xE into timeout counter register to
set the maximum timeout. The value is not correct for uSDHC since the
max counter value for uSDHC is 0xF.
Instead of using common timeout code in sdhci, we implement esdhc_set_timeout
to handle the difference between eSDHC and uSDHC.

Currently we simply set the max timeout value as before.
But in the future, we probably may implement IMX specific timeout
setting algorithm and use suitable timeout for different CMDs.

Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Dong Aisheng <b29396@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>