drm/amd: Move microcode init from sw_init to early_init for SDMA v2.4

As part of IP discovery early_init is run for all HW IP blocks.
During this phase all firmware is supposed to be identified that may
be missing so that the driver can avoid releasing resources used by
the EFI framebuffer or simpledrm until the last possible moment.

Move microcode loading from sw_init to early_init.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>