While there are cards with more than 8 mem banks, the max
number of banks from a tiling perspective is 8, so cap
the tiling config at 8 banks.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=43448Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: NDave Airlie <airlied@redhat.com>