msm: kgsl: Add stubs for pgprot macros to facilitate arm64

arm64 does not have certain pgprot macros and only supports
writeback caching. However, these pgprot caching macros are needed
by certain targets and need to be restored on mainline.
Therefore, we add the stubs to facilitate compilation in arm64.

Change-Id: I55949f31421409549c6e306d9771c652d82fe885
Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>