drm/amdgpu/gfx: decouple the number of kgqs from the hw

The driver currently sets up one kgq per pipe.  As such
adev->gfx.me.num_queue_per_pipe is hardcoded to 1 everywhere.
This is fine for kernel queues, but when we enable user queues
we need to know that actual number of queues per pipe.  Decouple
the kgq setup from the actual hardware count.  For dev core
dumps and user queues, we want to know the actual number
of queues per pipe.

Reviewed-by: Sunil Khatri <sunil.khatri@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>