drm/amdgpu/gfx9: Switch baremetal to use KIQ for compute ring management. (v4)

KIQ is the Kernel Interface Queue for managing the MEC.  Rather than setting
up rings via direct MMIO of ring registers, the rings are configured via
special packets sent to the KIQ.  The allows the MEC to better manage shared
resources and certain power events. It also reduces the code paths in the
driver to support and is required for MEC powergating.

v2: drop gfx_v9_0_cp_compute_fini() as well
v3: rebase on latest changes derived from gfx8, add unmap queues on
hw_fini
v4: fix copy/paste typo in error message (Rex)
Acked-by: Tom St Denis <tom.stdenis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>