[S390] kdump: Add size to elfcorehdr kernel parameter

Currently only the address of the pre-allocated ELF header is passed with
the elfcorehdr= kernel parameter. In order to reserve memory for the header
in the 2nd kernel also the size is required. Current kdump architecture
backends use different methods to do that, e.g. x86 uses the memmap= kernel
parameter. On s390 there is no easy way to transfer this information.
Therefore the elfcorehdr kernel parameter is extended to also pass the size.
This now can also be used as standard mechanism by all future kdump
architecture backends.

The syntax of the kernel parameter is extended as follows:

elfcorehdr=[size[KMG]@]offset[KMG]

This change is backward compatible because elfcorehdr=size is still allowed.

Acked-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

Documentation/kernel-parameters.txt

@@ -741,10 +741,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			See Documentation/block/cfq-iosched.txt and
 			Documentation/block/deadline-iosched.txt for details.
 
-	elfcorehdr=	[IA-64,PPC,SH,X86]
+	elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
 			Specifies physical address of start of kernel core
-			image elf header. Generally kexec loader will
-			pass this option to capture kernel.
+			image elf header and optionally the size. Generally
+			kexec loader will pass this option to capture kernel.
 			See Documentation/kdump/kdump.txt for details.
 
 	enable_mtrr_cleanup [X86]