mmc: sdhci-msm: Make clk gating a delayed work

With MMC_CAP_SYNC_RUNTIME_PM enabled now host suspend would
happen just after host release and it would make clk gating
very aggressive, which would have performance impact.

Make sdcc clk gating a delayed work to support
MMC_CAP_SYNC_RUNTIME_PM.

Change-Id: I9cf7c895e3dbcc494564389c916b6dd61f5fc22d
Signed-off-by: Ram Prakash Gupta <rampraka@codeaurora.org>