drm/amdgpu: implement vcn_v1_0_(dec|enc)_ring_emit_reg_wait v2

Add emit_reg_wait implementation for VCN v1.

v2: cleanup the existing code as well

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>