msm: kgsl: Add a cmdbatch profiling flag to get time since boot

Add a new cmdbatch profiling flag that populates the seconds
and nanosecond fields of the cmdbatch structure with the time
since boot instead of the wall time.

CRs-Fixed: 968114
Change-Id: I4e752d5237a74192b3ea9cc125c11bae574c1b36
Signed-off-by: Jonathan Wicks <jwicks@codeaurora.org>