drm/amdkfd: unmap VMID<-->PASID when relesing VMID (non-HWS)

This patch fixes a bug where deallocate_vmid() didn't actually unmap the
VMID<-->PASID mapping (in the registers).
That can cause undefined behavior.

This bug only occurs in non-HWS mode.

Signed-off-by: Ben Goz <ben.goz@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>