msm: kgsl: Use per page cache operation instead of bulk cache operation

For any cache operation, the current code tries to map all pages to the
kernel using vmap in case sg table is not available and then performs
the requested cache operation. If vmap fails because of memory crunch
ioctl just returns failure.

This change avoids using vmap and performs per page cache operation
even when sg table is not available. This is done to avoid failures
because of vmap especially on 32 bit systems.

Change-Id: I123b46e6a55a62cbf934ab6a2a49dcd1f0d4c7d4
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>