mmc: sdhci-msm: Restore SDCC Registers After CX Power Collapse

On some targets, the SDCC register contents are not retained
after resuming from a CX Power Collapse event. As a result, the
SD/SDIO/eMMC would fail to resume normal operation. This change allows
software to save and restore the SDCC register contents following a
CX Power Collapse event. On targets that the SDCC register contents
are retained by hardware, the software save-and-restore feature
can be disabled using the associated flag in the device tree file.

Change-Id: Ib03af741cd4818971e6b9b9b390724e1b0c4e5cc
Signed-off-by: Bao D. Nguyen <nguyenb@codeaurora.org>