s390/kdump: Do not add standby memory for kdump

Standby memory that is located outside [0,OLDMEM_SIZE] is currently used
by the s390 memory detection. This leads to additional memory consumption
due to allocation of page structures. To fix this, we now do not
add standby memory if the kernel is started in kdump mode.
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/char/sclp_cmd.c

@@ -627,6 +627,8 @@ static int __init sclp_detect_standby_memory(void)
 	struct read_storage_sccb *sccb;
 	int i, id, assigned, rc;
 
+	if (OLDMEM_BASE) /* No standby memory in kdump mode */
+		return 0;
 	if (!early_read_info_sccb_valid)
 		return 0;
 	if ((sclp_facilities & 0xe00000000000ULL) != 0xe00000000000ULL)