mmc: dw_mmc: add support for eMMC Power Off Notify feature

This patch adds the capability of power off notify for dw-mmc controller.
In order to use Girish's patch:
mmc: core: Add Power Off Notify Feature eMMC 4.5

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Will Newton <will.newton@imgtec.com>
Signed-off-by: Chris Ball <cjb@laptop.org>