Only the render backends of the first shader engine were enabled. The others
were erroneously disabled. Enabling the other render backends improves
performance a lot.

Unigine Sanctuary on Bonaire:
  Before: 15 fps
  After:  90 fps

Judging from the fan noise, the GPU was also underclocked when the other
render backends were disabled, resulting in horrible performance. The fan is
a lot noisy under load now.
Signed-off-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org