drivers/elog: put back 4KiB limit

The removal of ELOG_FLASH_BASE and ELOG_FLASH_SIZE resulted
in the FMAP region for the eventlog to be honored. However,
certain systems seem to have a large eventlog region that
wasn't being used in practice. Because of the malloc() in the
eventlog init sequence a large allocation was now being requested
that can exhaust the heap. Put back the 4KiB capacity until
the resource usage is fixed.

BUG=chrome-os-partner:55593

Change-Id: Ib54b396b48e5be80f737fc3feb0d58348c0d2844
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/15835
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/drivers/elog/elog.c

@@ -499,7 +499,8 @@ static void elog_find_flash(void)
 		flash_base = total_size = 0;
 	} else {
 		flash_base = region_offset(&r);
-		total_size = region_sz(&r);
+		/* Keep 4KiB max size until large malloc()s have been fixed. */
+		total_size = MIN(4*KiB, region_sz(&r));
 	}
 
 	log_size = total_size - sizeof(struct elog_header);