AGESA: Reduce SPI use by 24kB for S3 support

There is no need to backup VolatileStorage in SPI flash at all.
At the time we need it, we have CBMEM available.

Change-Id: If0ca57b314140a833d6d59fe9e236e07816f05a4
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/10318
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Edward O'Callaghan <edward.ocallaghan@koparo.com>

src/cpu/amd/agesa/heapmanager.c

@@ -49,7 +49,6 @@ void EmptyHeap(void)
 void ResumeHeap(void **heap, size_t *len)
 {
 	void *base = GetHeapBase();
-	memset(base, 0, BIOS_HEAP_SIZE);
 	*heap = base;
 	*len = BIOS_HEAP_SIZE;
 }