drm/amdgpu: add emit reg write reg wait for vcn jpeg

The emit_reg_write_reg_wait function was not assigned for vcn jpeg.
This patch adds it back.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Leo Liu <leo.liu at amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>