Add an early_init phase to MES for fetching and validating microcode
from the filesystem.

If MES microcode is required but not available during early init, the
firmware framebuffer will have already been released and the screen will
freeze.

Move the request for MES microcode into the early_init phase
so that if it's not available, early_init will fail.
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>