mmc: sdhci-of-esdhc: support both BE and LE host controller

To support little endian eSDHC controller, we redefine both BE and
LE IO accessors. In the new accessors, use ioread*/iowrite* instead
of in_be32/out_be32 and will select accessors according to endian
mode in probe function.

Signed-off-by: Yangbo Lu <yangbo.lu@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>