s390: move ipl block and cmd line handling to early boot phase

To distinguish zfcpdump case and to be able to parse some of the kernel
command line arguments early (e.g. mem=) ipl block retrieval and command
line construction code is moved to the early boot phase.

"memory_end" is set up correctly respecting "mem=" and hsa_size in case
of the zfcpdump.

arch/s390/boot/string.c is introduced to provide string handling and
command line parsing functions to early boot phase code for the compressed
kernel image case.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/boot_data.h

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_BOOT_DATA_H
+
+#include <asm/setup.h>
+#include <asm/ipl.h>
+
+extern char early_command_line[COMMAND_LINE_SIZE];
+extern struct ipl_parameter_block early_ipl_block;
+extern int early_ipl_block_valid;
+
+#endif /* _ASM_S390_BOOT_DATA_H */