drm/amdgpu: attempt to enable gfxoff on more raven1 boards (v2)

Switch to a blacklist so we can disable specific boards
that are problematic.

v2: make the blacklist non-raven specific.

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>