mmc: sdhci-msm: Add bus aggregate clock for sdhc platform driver

Some targets have sdhc controllers which require bus aggregate clock to
be on for DMA transfer to work. Add support to enable this clock during
initialization and also enable/diasble it during resume/suspend of the
controller clocks.

Change-Id: I579803e0efc248918e12925ea7fbc24e9be3b59d
Signed-off-by: Vijay Viswanath <vviswana@codeaurora.org>