mmc: sdhci-s3c: derive transfer width host cap from max_width in platdata

max_width member in platform data can be used to derive the mmc bus transfer
width that can be supported by the controller.

Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>