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>