msm: kgsl: Add fallback condition for atomic snapshot

There is possibility of failure in getting large memory
during panic notifier callback. Hence try atomic snapshot
with 1MB in case default memory allocation fails.

Change-Id: I8f5ff29139d272dc35094c230e1868623585b476
Signed-off-by: Rohan Sethi <rohsethi@codeaurora.org>