drm/amdgpu: Add kernel parameter support for ignoring bad page threshold

When a GPU hits the bad_page_threshold, it will not be initialized by
the amdgpu driver. This means that the table cannot be cleared, nor can
information gathering be performed (getting serial number, BDF, etc).

If the bad_page_threshold kernel parameter is set to -2,
continue to initialize the GPU, while printing a warning to dmesg that
this action has been done

v2: squash in Luben's fix to restore RAS info reporting

Cc: Luben Tuikov <luben.tuikov@amd.com>
Cc: Mukul Joshi <Mukul.Joshi@amd.com>
Signed-off-by: Kent Russell <kent.russell@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>