s390/vmcoreinfo: Store virtual memory layout

This is a preparatory rework to allow uncoupling virtual
and physical addresses spaces.

The virtual memory layout is needed for address translation
by crash tool when /proc/kcore device is used as the memory
image.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>