msm: kgsl: Optimally reserve CP context record size for A6xx GPUs

Currently CP context record size is fixed for all A6xx GPUs i.e 2112KB
per ringbuffer. But for low end GPUs this memory is not really useful
and becomes unnecessary in case of low memory devices.

Overall context record size includes GPU HW state and GMEM size.

This change reserves the context record size by considering the
actual GMEM size instead of default 1MB for GMEM.

Change-Id: I9f050fabba903922e7a61b89f8652f08c66fcdb0
Signed-off-by: Rajesh Kemisetti <rajeshk@codeaurora.org>