drm/amdgpu: move per inst variables to amdgpu_vcn_inst

Move all per instance variables from amdgpu_vcn to amdgpu_vcn_inst.

Move adev->vcn.fw[i] from amdgpu_vcn to amdgpu_vcn_inst.
Move adev->vcn.vcn_config[i] from amdgpu_vcn to amdgpu_vcn_inst.
Move adev->vcn.vcn_codec_disable_mask[i] from amdgpu_vcn to amdgpu_vcn_inst.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>