drm/amdgpu/gmc9: use amdgpu_ring_emit_reg_write_reg_wait in gpu tlb flush

Use amdgpu_ring_emit_reg_write_reg_wait.  On engines that support it,
it provides a write and wait in a single packet which avoids a missed
ack if a world switch happens between the request and waiting for the
ack.

Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>