drm/msm/a6xx: Use descriptive bitfield names for CP_PROTECT_CNTL

We have the necessary information, so explain which bit does what.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/543332/


Signed-off-by: Rob Clark <robdclark@chromium.org>