msm: kgsl: Increase REG_RBBM_CNTL value to 0xFFFF for A20X

Increase number of clocks that RBBM will wait before de-asserting
the Register Clock Active signal. This fixes kernel panics during
stability tests on multiple devices

Change-Id: I6f7f8bb17cfd9c5beed0fd21d56ab6ab9fd40195
Signed-off-by: Rammohan Basavaraju <rammoh@codeaurora.org>
Signed-off-by: Rajeev Kulkarni <krajeev@codeaurora.org>