drm/amd: Convert SMUv13 microcode to use `amdgpu_ucode_ip_version_decode`

The special case for the one dGPU has been moved into
`amdgpu_ucode_ip_version_decode`, so simplify this code.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>