drm/amdgpu: implement vce_v4_0_emit_reg_wait v2

Add emit_reg_wait implementation for VCE v4.

v2: call new function directly from existing code

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>