drm/amd/display: Load DMUB microcode during early_init

If DMUB is required for an ASIC, ensure that the microcode is available
and validates during early_init.

Any failures will cause the driver to fail to probe before the firmware
framebuffer has been removed.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@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>