powerpc: Use generic wcsrchr optimization

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