drm/amdgpu: add generic pci reset as an option

This allows us to use generic PCI reset mechanisms (FLR, SBR) as
a reset mechanism to verify that the generic PCI reset mechanisms
are working properly.

Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>