drm/amdgpu: mv some definition from amdgpu_acpi.c to amdgpu_acpi.h

These will be shared with the new powerplay module.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>