drm/amd: Don't parse IMU ucode version if it won't be loaded

When the IMU ucode is loaded by the PSP parsing the version that comes from
Linux will vary. Rather than showing the wrong data to kernel interface
consumers, avoid populating it in this case.

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>