drm/amd: Move microcode init step to early_init()

The intention for early init is to find any missing microcode early
and fail the driver load if it's missing.  Move this step to earlier
in driver init to match other IP blocks.

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>