s390/kexec: fix update of os_info crash kernel size

Implement an s390 version of the weak crash_free_reserved_phys_range
function. This allows us to update the size of the reserved crash
kernel memory if it will be resized.

This was previously done with a call to crash_unmap_reserved_pages
from crash_shrink_memory which was removed with ("s390/kexec:
consolidate crash_map/unmap_reserved_pages() and
arch_kexec_protect(unprotect)_crashkres()")

Fixes: 7a0058ec ("s390/kexec: consolidate crash_map/unmap_reserved_pages() and arch_kexec_protect(unprotect)_crashkres()")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>