mmc: sdhci-msm: Disable pm functionalities

Disable the following pm functionalities till they are functional:
 * clk scaling (need to verify full functionality)
 * clk gating (crashes when ungating the clock)

Change-Id: I0962d46d85415e77b978e1f7dd9f2f49446655bb
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>