msm: kgsl: fix accounting of memory mapped to userspace

The mapsize of kgsl_memdesc and gpumem_mapped of process are
incremented only in vmfault handler. But for cache modes
write through and write back, pages are inserted in kgsl_mmap.
So account for those mappings also in gpumem_mapped.

Change-Id: I98e29b28fa6fd2915b03bdcb9c655015a926d0eb
Signed-off-by: Puranam V G Tejaswi <pvgtejas@codeaurora.org>