Move the `mainboard_fill_spd_data` function out of romstage, in
preparation to confine `pei_data` usage to as few files as possible.
Change-Id: I6447da4d135d920f9145e817bfb7f9056e09df84
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55805
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>