msm: kgsl: Add Common Boot KPI marker

Add a boot marker to indicate the time when gpu
driver probe is completed and the device is ready,
and adreno driver is initialised and ready for a640.

Change-Id: I1bfd133b9f23dd497d2ab13cde4989b922ab47a7
Signed-off-by: Rituraj Raman <riturama@codeaurora.org>