s390/ptrace: always include vector registers in core files

On machines with support for vector registers the signal frame includes
an area for the vector registers and the ptrace regset interface allow
read and write. This is true even if the task never used any vector
instruction. Only elf core dumps do not include the vector registers,
to make things consistent always include the vector register note in
core dumps create on a machine with vector register support.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>