mmc: Add SD Status register to debugfs

mmc: Add SD Status register to debugfs

BZ:  5522

This patch add the SD status register to debugfs. SD Status register is
a SD card register which contains status bits that are related to the SD
Memory Card proprietary features and may be used by future application-specific
usge, it is helpful to see its value.

Change-Id: Ia9041833bd432bd37df9e1d846aa66a856b19efc
Signed-off-by: Hao Ying <hao.ying@intel.com>
Reviewed-on: http://android.intel.com:8080/23128
Reviewed-by: Gross, Mark <mark.gross@intel.com>
Tested-by: Gross, Mark <mark.gross@intel.com>