drm/amd: Add a legacy mapping to "amdgpu_ucode_ip_version_decode"

This will allow other parts of the driver that currently special
case firmware file names to before IP version style naming to just
have a single call to `amdgpu_ucode_ip_version_decode`.

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>