msm: kgsl: Dump maximum possible IB1 size in snapshot

Currently adreno_snapshot() tries to dump remaining IB1 size
if the active IB1 base address is not present in ringbuffer
which is not enough to debug GPU hang.

So, try to calculate the maximum possible size that it can
dump from IB1 base address and add it to snapshot dump.

Change-Id: I029fb8cddab7999001a2934ce49cb5ff884c21bf
Signed-off-by: Rajesh Kemisetti <rajeshk@codeaurora.org>