mmc: core: support HPI send command

mmc: core: support HPI send command

HPI command is defined in eMMC4.41. This patch implements sending
HPI command to eMMC card if card supports.

Besides these changes, this patch also exported some sysfs which can
be used check whether the hpi is supported easily

Change-Id: I14ad85fe47a080564731228c3fe816f4f0b847eb
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Reviewed-on: http://android.intel.com:8080/23121
Reviewed-by: Gross, Mark <mark.gross@intel.com>
Tested-by: Gross, Mark <mark.gross@intel.com>