S390: Add z13 memmove ifunc variant.

S390: Add z13 memmove ifunc variant.

This patch introduces a z13 specific ifunc variant for memmove.
As the common code implementation, it checks if we can copy from
the beginning to the end - with z196 memcpy implementation - or
if we have to copy from the end to the beginning.
The latter case is done by using vector load/store instructions.

If vector instructions are not available, the common-code is
used as fallback.  Therefore it is implemented in memmove-c with
a different name.
Furthermore the ifunc logic decides if we need the common-code
implementation at all.  If vector instructions are supported
due to the minimum architecture level set we can skip the
common-code ifunc variant.

ChangeLog:

	* sysdeps/s390/Makefile (sysdep_routines): Add memmove-c.
	* sysdeps/s390/ifunc-memcpy.h (HAVE_MEMMOVE_IFUNC,
	HAVE_MEMMOVE_IFUNC_AND_VX_SUPPORT, MEMMOVE_DEFAULT,
	HAVE_MEMMOVE_C, MEMMOVE_C,  HAVE_MEMMOVE_Z13, MEMMOVE_Z13):
	New defines.
	* sysdeps/s390/memcpy-z900.S: Add z13 memmove implementation.
	* sysdeps/s390/memmove-c.c: New file.
	* sysdeps/s390/memmove.c: Likewise.
	* sysdeps/s390/multiarch/ifunc-impl-list.c
	(__libc_ifunc_impl_list): Add ifunc variants for memmove.