msm: kgsl: Fill a6xx crash dumper buffer with known pattern

Sometimes crashdumper can timeout due to  unresponsive hang
scenarios. Hence fill the crash dumper with known pattern to
know the progress of crashdumper before it gets timed out.

Change-Id: I757fa345b4d7db7d7012ff6501b169a562f9b9c6
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>