msm: kgsl: Enable content protection for A506

Enable content protection for A506 from gpulist.

Also, skip scm call to program CP secure ucode base
registers since A506 supports retention for these
registers.

Change-Id: I48a0f04826430bfb927c755c176255be45199b26
Signed-off-by: Rajesh Kemisetti <rajeshk@codeaurora.org>