mmc: block: add support for partition switch

There could be a switch of partition while RPMB access.
RPMB thread would then hand-off the control to mmc-cmdq-thread
in the following state:
	- partition set to RPMB in card
	- CMDQ mode disabled in card
	- Controller in halt state

When the next request is received, the following has to be done
	- switch partition to the current partition
	- enable CMDQ in card
	- unhalt controller

Change-Id: I9eca350572fd88476dfee9642696a223c5cd7ada
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>