drm/amd: Load VCN microcode during early_init

Simplifies the code so that all VCN versions will get the firmware
name from `amdgpu_ucode_ip_version_decode` and then use this filename
to load microcode as part of the early_init process.

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