arch/powerpc: Remove duplicate/redundant Altivec entries

In lieu of having multiple similiar lines, we can just have one
generic cpu-as line for CONFIG_ALTIVEC
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/Makefile

@@ -131,8 +131,7 @@ KBUILD_CFLAGS		+= -mno-sched-epilog
 endif
 
 cpu-as-$(CONFIG_4xx)		+= -Wa,-m405
-cpu-as-$(CONFIG_6xx)		+= -Wa,-maltivec
-cpu-as-$(CONFIG_POWER4)		+= -Wa,-maltivec
+cpu-as-$(CONFIG_ALTIVEC)	+= -Wa,-maltivec
 cpu-as-$(CONFIG_E500)		+= -Wa,-me500
 cpu-as-$(CONFIG_E200)		+= -Wa,-me200