s390/mem_detect: use SCLP info for continuous memory detection

When neither SCLP storage info, nor z/VM diag260 "storage configuration"
are available assume a continuous online memory of size specified by
SCLP info.

Reviewed-by: Heiko Carstens <[e-mail]>
Reviewed-by: Martin Schwidefsky <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/boot/mem_detect.c

···
 		return;
 	}
 
+	if (max_physmem_end) {
+		add_mem_detect_block(0, max_physmem_end);
+		mem_detect.info_source = MEM_DETECT_SCLP_READ_INFO;
+		return;
+	}
+
 	scan_memory(rzm);
 	mem_detect.info_source = MEM_DETECT_TPROT_LOOP;
-	if (!max_physmem_end)
-		max_physmem_end = get_mem_detect_end();
+	max_physmem_end = get_mem_detect_end();
 }

arch/s390/include/asm/mem_detect.h

···
 	MEM_DETECT_NONE = 0,
 	MEM_DETECT_SCLP_STOR_INFO,
 	MEM_DETECT_DIAG260,
+	MEM_DETECT_SCLP_READ_INFO,
 	MEM_DETECT_TPROT_LOOP
 };