msm: kgsl: use the wall clock for the user profiling buffer

Use getnstimeofday() to get the current wall clock value to return
to the user in the cmdbatch profiling buffer.  This lets them match
up the submit time with gettimeofday() on the user side.

CRs-fixed: 731844
Change-Id: Ic0dedbadac053cc5c97806465760e2fc0ec69d34
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>