powerpc: Use generic wcscpy optimization

This patch removes the power6 wcscpy optimization and uses generic
implementation instead.  Currently, both power6 and power7 IFUNC variant
resulting binary are essentially the same and the generic implementation
with unrolling loop set to 8 also results in similar performance.

Checked on powerpc64-linux-gnu.

	* sysdeps/powerpc/Makefile [$(subdir) == wcsmbs] (CFLAGS-wcscpy.c):
	New rule.
	* sysdeps/powerpc/power6/wcscpy.c: Remove file.
	* sysdeps/powerpc/powerpc32/power4/multiarch/wcscpy-power6.c:
	Likewise.
	* sysdeps/powerpc/powerpc32/power4/multiarch/wcscpy-power7.c:
	Likewise.
	* sysdeps/powerpc/powerpc32/power4/multiarch/wcscpy-ppc32.c:
	Likewise.
	* sysdeps/powerpc/powerpc32/power4/multiarch/wcscpy.c: Likewise.
	* sysdeps/powerpc/powerpc64/multiarch/wcscpy-power6.c: Likewise.
	* sysdeps/powerpc/powerpc64/multiarch/wcscpy-power7.c: Likewise.
	* sysdeps/powerpc/powerpc64/multiarch/wcscpy-ppc64.c: Likewise.
	* sysdeps/powerpc/powerpc64/multiarch/wcscpy.c: Likewise.
	* sysdeps/powerpc/powerpc64/power6/wcscpy.c: Likewise.
	* sysdeps/powerpc/powerpc32/power4/multiarch/Makefile
	[$(subdir) == wcsmbs] (sysdeps_routines): Remove wcscpy-power6 and
	wcscpy-power7.
	(CFLAGS-wcscpy-power7.c, CFLAGS-wcscpy-power6.c): Remove rule.
	* sysdeps/powerpc/powerpc64/multiarch/Makefile: Likewise.
	* sysdeps/powerpc/powerpc32/power4/multiarch/ifunc-impl-list.c:
	Remove wcscpy optimizations.
	* sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c: Likewise.