msm: kgsl: Update preemption context record size for a660

Add per a6xx target member to specify the preemption record size
in case it is different than the default size for all a6xx.

Change-Id: I6e5579eae47dc4ee6707437d858b8b969fe573ea
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>