drm/amdgpu: expose GPU sensor related information

This includes shader/memory clocks, temperature, GPU load, etc.

v2: - add sub-queries for AMDPGU_INFO_GPU_SENSOR_*
    - do not break the ABI
v3: - return -ENOENT when amdgpu_dpm == 0
    - expose more sensor queries
v4: - s/GPU_POWER/GPU_AVG_POWER/
    - improve VDDNB/VDDGFX query description
    - fix amdgpu_dpm check
v5: - agd: fix warning
v6: - agd: bump version

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>