[coreboot] Please test and review AGESA code

[Arthur Heymans]

Hi

We spend more time debating whether to keep AGESA in the master branch than
actually reviewing code to maintains it.

Here are some patches series I would like to be tested & reviewed:

- Agesa was never properly linked and relied on default linker behavior
   to append unmatched data. Here is the fix:
   https://review.coreboot.org/q/topic:AGESA_DATA
   - Use MRC cache for non volatile data
   https://review.coreboot.org/q/topic:AGESA_MRC_CACHE
   - Use CLFLUSH to make sure code hits DRAM and incidently avoid
   inconsistent MTRRs (bonus is compressed postcar stage):
   https://review.coreboot.org/q/topic:compress_postcar

Kind regards
Arthur