drm: msm: a6xx: Add support for A618

This patch adds support for enabling Graphics Bus Interface(GBIF)
used in multiple A6xx series chipets. Also makes changes to the
PDC/RSC sequencing specifically required for A618. This is needed
for proper interfacing with RPMH.

Signed-off-by: Sharat Masetty <smasetty@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>