s390/kdump: Use "LINUX" ELF note name instead of "CORE"

In binutils/libbfd (bfd/elf.c) it is enforced that all s390 specific ELF
notes like e.g. NT_S390_PREFIX or NT_S390_CTRS have "LINUX" specified
as note name. Otherwise the notes are ignored.

For /proc/vmcore we currently use "CORE" for these notes.

Up to now this has not been a real problem because the dump analysis tool
"crash" does not check the note name. But it will break all programs that
use libbfd for processing ELF notes.

So fix this and use "LINUX" for all s390 specific notes to comply with
libbfd.

Cc: stable@vger.kernel.org # v4.4+
Reported-by: Philipp Rudo <prudo@linux.vnet.ibm.com>
Reviewed-by: Philipp Rudo <prudo@linux.vnet.ibm.com>
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>