mmc: core: add background operations for eMMC card

mmc: core: add background operations for eMMC card

Driver will check if need to do a BKOPS after completed each
user request. If BKOPS is need, then will start BKOPS when
request queue is idle.

So before start user request, driver should also check whether
card is doing a BKOPS. If so, check card status until BKOPS is done
or send HPI command is supported.

Change-Id: I204fab3d124c5a209cb0cc3a2915380a31c22b79
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Reviewed-on: http://android.intel.com:8080/23123
Reviewed-by: Gross, Mark <mark.gross@intel.com>
Tested-by: Gross, Mark <mark.gross@intel.com>