drm/msm/gpu: Move zap shader loading to adreno

a5xx and a6xx both share (mostly) the same code to load the zap shader and
bring the GPU out of secure mode. Move the formerly 5xx specific code to
adreno to make it available for a6xx too.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>