Revert "drm/amdgpu: Program xcp_ctl registers as needed"

This reverts commit 0bdebfef.

XCP_CTL register is programmed by firmware and
register access is protected.

Signed-off-by: Mangesh Gadre <Mangesh.Gadre@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>