drm/amdgpu: add function to show ucode name via id

Implement function amdgpu_ucode_name to show ucode name
via ucode id.

v2: rename it to amdgpu_ucode_name

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