amd/pi: Add GetTempHeapBase callout

Implement a new AGESA callout that may be used to find the correct
temporary location in DRAM to store heap data.

Near the end of AmdInitPost, AGESA migrates its heap from a CAR-based
location to a temporary region.  Once cbmem has been established, the
heap will be relocated again in AmdInitEnv from the temp location to
the final one.

This patch does not materially affect the behavior of AGESA's heap
management.  It only puts coreboot in control of the location.  Future
work may refactor the copying.

TEST=Boot grunt with patchstack and experimental blob
BUG=b:74518368

Change-Id: Ibc5cc988e3e80d78f50cf0195e952b657141e570
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/26146
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
4 files changed