powerpc: remove redundant header search path additions

The same path -Iarch/$(ARCH) is passed to KBUILD_CPPFLAGS,
KBUILD_AFLAGS, and KBUILD_CFLAGS.

As you see in scripts/Makefile.lib, KBUILD_CPPFLAGS is passed
to c_flags and a_flags as well.

Passing it to KBUILD_CPPFLAGS is enough.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Makefile

@@ -213,9 +213,9 @@ endif
 asinstr := $(call as-instr,lis 9$(comma)foo@high,-DHAVE_AS_ATHIGH=1)
 
 KBUILD_CPPFLAGS	+= -Iarch/$(ARCH) $(asinstr)
-KBUILD_AFLAGS	+= -Iarch/$(ARCH) $(AFLAGS-y)
+KBUILD_AFLAGS	+= $(AFLAGS-y)
 KBUILD_CFLAGS	+= $(call cc-option,-msoft-float)
-KBUILD_CFLAGS	+= -pipe -Iarch/$(ARCH) $(CFLAGS-y)
+KBUILD_CFLAGS	+= -pipe $(CFLAGS-y)
 CPP		= $(CC) -E $(KBUILD_CFLAGS)
 
 CHECKFLAGS	+= -m$(BITS) -D__powerpc__ -D__powerpc$(BITS)__