drm/amdgpu: add VPE firmware interface

Add initial firmware interface. (Ray)
Add more opcodes and rename to vpe_v6_1. (Lang)

v2: Update copyright date (Alex)

Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Lang Yu <Lang.Yu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>