soc/amd/stoneyridge: Add postcar stage

Insert a postcar stage for Stoney Ridge and move romstage's CAR
teardown there.

The AMD cache-as-ram teardown procedure currently uses a wbinvd
instruction to send CAR contents to DRAM backing.  This allows
preserving stack contents and CAR globals after the teardown
happens, but likely results in memory corruption during S3 resume.
Due to the current base of the DCACHE region, reverting to an
invd instruction will break the detection mechanism for CAR
migrated variables.  Using postcar avoids this problem.

The current behavior of AGESA is to set up all cores' MTRRs during
the AmdInitPost() entry point.  This implementation takes control
back and causes postcar's _start to clear all settings and set
attributes only for the BIOS flash device, TSEG, and enough space
below cbmem_top to load and run ramstage.

BUG=b:64768556

Change-Id: I1045446655b81b806d75903d75288ab17b5e77d1
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/20966
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
5 files changed