drm/amdgpu: add perfmons accessible during df c-states

During DF C-State, Perfmon counters outside of range 1D700-1D7FF will
encounter SLVERR affecting xGMI performance monitoring.  PerfmonCtr[7:4]
is being added to avoid SLVERR during read since it falls within this
range.  PerfmonCtl[7:4] is being added in order to arm PerfmonCtr[7:4].
Since PerfmonCtl[7:4] exists outside of range 1D700-1D7FF, DF routines
will be enabled to opportunistically re-arm PerfmonCtl[7:4] on retry
after SLVERR.

Signed-off-by: Jonathan Kim <Jonathan.Kim@amd.com>
Acked-by: Alex Deucher <Alexander.Deucher@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>