AGESA boards: Fix regressions with LATE_CBMEM_INIT

Some configurations of AGESA boards fail to boot after commit
  61be360 AGESA: Fix UMA calculations

Implementation of cbmem_find() for ENV_ROMSTAGE expects
that CBMEM has already been initialized. In the case of
LATE_CBMEM_INIT boards, this is not the case and cbmem_top()
returned NULL prior to the offending commmit.

By definition LATE_CBMEM_INIT does not have known cbmem_top()
in ENV_ROMSTAGE except for possible ACPI S3 resume path.

Change-Id: Icb8f44661d479e5ad43b123600305dcbc3ce11e1
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/20590
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/arch/x86/cbmem.c

@@ -45,6 +45,10 @@ void set_late_cbmem_top(uintptr_t ramtop)
 /* Top of CBMEM is at highest usable DRAM address below 4GiB. */
 uintptr_t __attribute__((weak)) restore_cbmem_top(void)
 {
+	if (IS_ENABLED(CONFIG_LATE_CBMEM_INIT) && ENV_ROMSTAGE)
+		if (!acpi_is_wakeup_s3())
+			return 0;
+
 	return restore_top_of_low_cacheable();
 }