drm/amdgpu: Add infrastructure for Cleaner Shader feature

The cleaner shader is used by the CP firmware to clean LDS and GPRs
between processes on the CUs.

This adds an internal API for GFX IP code to allocate and initialize the
cleaner shader.

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Suggested-by: Christian König <christian.koenig@amd.com>