msm: kgsl: correct per process stat maintenance

In functions like gpumem_alloc_entry(), per process
stats are updated after kgsl_mem_entry_attach_process()
returns success. But in case of failure, per process
stats are decremented, though they are not incremented.
Fix this by isolating stat updation from
kgsl_mem_entry_detach_process(). Also take into account
the memory from sparse allocations.

Change-Id: I6e2bc1880bdda15aa75d546d0dc3d34c63cd7dba
Signed-off-by: Puranam V G Tejaswi <pvgtejas@codeaurora.org>