powerpc: Use generic wcschr optimization

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