x86: fix boot error introduced by kbuild

x86 uses target specific assignment of EXTRA_AFLAGS,
EXTRA_CFLAGS - this caused troubles with
introducing asflags-y, ccflags-y.

Fixed the target specific assignments in arch/x86/boot/Makefile
and auditted the rest of the kernel for similar usage.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

arch/x86/boot/Makefile

@@ -64,10 +64,10 @@ KBUILD_CFLAGS	:= $(LINUXINCLUDE) -g -Os -D_SETUP -D__KERNEL__ \
 KBUILD_AFLAGS	:= $(KBUILD_CFLAGS) -D__ASSEMBLY__
 
 $(obj)/zImage:  IMAGE_OFFSET := 0x1000
-$(obj)/zImage:  EXTRA_AFLAGS := $(SVGA_MODE) $(RAMDISK)
+$(obj)/zImage:  asflags-y := $(SVGA_MODE) $(RAMDISK)
 $(obj)/bzImage: IMAGE_OFFSET := 0x100000
-$(obj)/bzImage: EXTRA_CFLAGS := -D__BIG_KERNEL__
-$(obj)/bzImage: EXTRA_AFLAGS := $(SVGA_MODE) $(RAMDISK) -D__BIG_KERNEL__
+$(obj)/bzImage: ccflags-y := -D__BIG_KERNEL__
+$(obj)/bzImage: asflags-y := $(SVGA_MODE) $(RAMDISK) -D__BIG_KERNEL__
 $(obj)/bzImage: BUILDFLAGS   := -b
 
 quiet_cmd_image = BUILD   $@