s390x: Add vector registers to ELF dump

Create ELF notes for the vector registers where applicable, so that
their contents can be examined by utilities such as crash or readelf.

Signed-off-by: Eric Farman <farman@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
