mmc: sdhci-msm: Fix the retention of DLL regs from CX Collapse

When exit from CX collapse event, the DLL registers lose their
contents because there is no SDCC registers retention support
during CX Collapse event. In case the SDCC is operating in
SDR104/HS200/HS400 modes, before resuming from CX Collapse event,
the DLL registers need to be saved and restored followed by
the SDCC's DLL initialization sequence in order for the DLL to be
fully functional again.

Change-Id: I9a870e783ce9b7271038fa5ce6e1d2f48a67d162
Signed-off-by: Bao D. Nguyen <nguyenb@codeaurora.org>