drm/amdgpu: Disable dpm_enabled flag while VF is in reset

VFs do not perform HW fini/suspend in FLR, so the dpm_enabled
is incorrectly kept enabled. Add interface to disable it in
virt_pre_reset call.

v2: Made implementation generic for all asics
v3: Re-order conditionals so PP_MP1_STATE_FLR is only evaluated on VF

Signed-off-by: Victor Skvortsov <victor.skvortsov@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>