mmc: enable boot partition accessing for CLV

mmc: enable boot partition accessing for CLV

BZ: 31365

UMIP driver needs to access boot partition from IA. So eMMC driver
needs to open the access for it

Change-Id: I73a6df32e0229f9a24469524ba4f248236ae0659
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Reviewed-on: http://android.intel.com:8080/43090
Reviewed-by: Tang, Richard <richard.tang@intel.com>
Reviewed-by: Gao, Yunpeng <yunpeng.gao@intel.com>
Tested-by: Sun, Jianhua <jianhua.sun@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>