drm/amdgpu: Fix deadlock during GPU reset.

Bug:
Kfifo is limited at size, during GPU reset it would fill up to limit
and the pushing thread (producer) would wait for the scheduler worker to
consume the items in the fifo while holding reservation lock
on a BO. The gpu reset thread on the other hand blocks the scheduler
during reset. Before it unblocks the sceduler it might want
to recover VRAM and so will try to reserve the same BO the producer
thread is already holding creating a deadlock.

Fix:
Switch from kfifo to SPSC queue which is unlimited in size.

Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>