drm/amdgpu: unify fw_write_wait for new gfx9 asics

Make the fw_write_wait default case true since presumably all new
gfx9 asics will have updated firmware. That is using unique WAIT_REG_MEM
packet with opration=1.

Signed-off-by: Aaron Liu <aaron.liu@amd.com>
Tested-by: Aaron Liu <aaron.liu@amd.com>
Tested-by: Yuxian Dai <Yuxian.Dai@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org