msm: 8064: Add regulator supply for DDR3 memory

PCDDR3 memory on 8064 platform requires PM8921 MPP7 pin
to be always high. Platforms with PCDDR3 memory will have
MPP7 pin set to output high by bootloaders.

However, MPP7 is already used as the enable signal for the 5V
boost regulator which supplies the HDMI and USB OTG switches.
In order to make sure that regulator disable requests from
these clients do not drive MPP7 low, add an addition regulator
enable call so that ref count of 5V regulator never goes to 0.

Change-Id: I8428f93a8ebf2a3a6763a90b4431f4573230e277
Signed-off-by: Jay Chokshi <jchokshi@codeaurora.org>