drm/amdgpu: revert "XGMI pstate switch initial support"

This reverts commit 9b638f97.

Adding this to the mapping is complete nonsense and the whole
implementation looks racy. This patch wasn't thoughtfully reviewed
and should be reverted for now.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Liu, Shaoyun <Shaoyun.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>