xx20/xx30 memory scrubbing on boot

Nobody has claimed this yet.

**Is your feature request related to a problem? Please describe.**
If not introducing way longer init, memory scrubbing should be activated in coreboot. Otherwise a reboot of machine might still include some secret in memory from last booted state where no guarantee are provided that they will be overwritten.

**Describe the solution you'd like**
Memory scrubbing within 2-5 additional seconds on boot (acceptable for added feature)

**Describe alternatives you've considered**
PoC was done from tails to scrub memory on shutdown (OS related) but was dropped AFAIK.

**Additional context**
Just a reminder for testing, at least on x230 (native init might work) was reported that on librems, it was vertically exponential by qty of ram installed. This would just validate possible interest and open debate to add it or not on older platforms not relaying on FSP for ram init. Yet just an hypothesis to validate.

Start by investigating coreboot's native memory initialization on xx20/xx30 platforms and validate the reported librems scrubbing time against installed RAM. The issue mentions an OS-level Tails proof of concept and a target of 2–5 additional seconds on boot; done would require measured feasibility and a decided implementation scope.

Written by the indexing model from the issue text.