ARM: dts: msm: Add bus voting entries for SDHC slots on MSM8939

Add bus bandwidth voting entries to SDHC slots to ensure optimum
bus performance while SDHC transfers are in progress.

Change-Id: I02443f63fedf9689a1a8f9ad9dfc35a9e18fab1f
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>