drm/amdgpu: add van gogh asic_type enum (v2)

This patch adds van gogh to amd_asic_type enum and amdgpu_asic_name[].

v2: add missing comma

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