drm/amdgpu: stop resetting xgmi perfmons on disable

Disabling perf events does not specify reset in ABI so stop doing it in
hardware.

Signed-off-by: Jonathan Kim <Jonathan.Kim@amd.com>
Reviewed-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>