kbuild: enable 'make AFLAGS=...' to add additional options to AS

The variable AFLAGS is a wellknown variable and the usage by
kbuild may result in unexpected behaviour.
On top of that several people over time has asked for a way to
pass in additional flags to gcc.

This patch replace use of AFLAGS with KBUILD_AFLAGS all over
the tree.

Patch was tested on following architectures:
alpha, arm, i386, x86_64, mips, sparc, sparc64, ia64, m68k, s390

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/arch/frv/Makefile b/arch/frv/Makefile
index ec89886..310c47a 100644
--- a/arch/frv/Makefile
+++ b/arch/frv/Makefile
@@ -63,16 +63,16 @@
 
 ifdef CONFIG_CPU_FR451_COMPILE
 KBUILD_CFLAGS	+= -mcpu=fr450
-AFLAGS		+= -mcpu=fr450
+KBUILD_AFLAGS	+= -mcpu=fr450
 ASFLAGS		+= -mcpu=fr450
 else
 ifdef CONFIG_CPU_FR551_COMPILE
 KBUILD_CFLAGS	+= -mcpu=fr550
-AFLAGS		+= -mcpu=fr550
+KBUILD_AFLAGS	+= -mcpu=fr550
 ASFLAGS		+= -mcpu=fr550
 else
 KBUILD_CFLAGS	+= -mcpu=fr400
-AFLAGS		+= -mcpu=fr400
+KBUILD_AFLAGS	+= -mcpu=fr400
 ASFLAGS		+= -mcpu=fr400
 endif
 endif
@@ -82,14 +82,14 @@
 # - all the extra registers are dealt with only at context switch time
 KBUILD_CFLAGS	+= -mno-fdpic -mgpr-32 -msoft-float -mno-media
 KBUILD_CFLAGS	+= -ffixed-fcc3 -ffixed-cc3 -ffixed-gr15 -ffixed-icc2
-AFLAGS		+= -mno-fdpic
+KBUILD_AFLAGS	+= -mno-fdpic
 ASFLAGS		+= -mno-fdpic
 
 # make sure the .S files get compiled with debug info
 # and disable optimisations that are unhelpful whilst debugging
 ifdef CONFIG_DEBUG_INFO
 #KBUILD_CFLAGS	+= -O1
-AFLAGS		+= -Wa,--gdwarf2
+KBUILD_AFLAGS	+= -Wa,--gdwarf2
 ASFLAGS		+= -Wa,--gdwarf2
 endif