drm/amdgpu: Exclude PCI reset method for now.

According to my investigation of the state of PCI
reset recently it's not working. The reason is
due to the fact the kernel PCI code rejects SBR
when there are more then one PF under same bridge
which we always have (at least AUDIO PF but usually
more) and that because SBR will reset all the PFS
and devices under the same bridge as you and you
cannot assume they support SBR.
Once we anble FLR support we can reenable this option as
FLR is doable on single PF and doens't have this
restriction.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>