drm/amdkfd: Use KIQ to unmap HIQ

Currently, we unmap HIQ by directly writing to HQD
registers. This doesn't work for GFX9.4.3. Instead,
use KIQ to unmap HIQ, similar to how we use KIQ to
map HIQ. Using KIQ to unmap HIQ works for all GFX
series post GFXv9.

Signed-off-by: Mukul Joshi <mukul.joshi@amd.com>
Reviewed-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>