sdhci: 8-bit data transfer width support

Some host controllers such as s5pc110 support the WIDE8 feature.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>