drm/amdgpu: acquire available gfx queues

currently, amdgpu will owns the first gfx queue of each pipe
they are:
me:0 pipe:0 queue:0
me:0 pipe:1 queue:0

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Jack Xiao <jack.xiao@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>