Revert "MIPS: boot: Define __ASSEMBLY__ for its.S build"

This reverts commit 0f9da844.

It is true that commit 0f9da844 ("MIPS: boot: Define __ASSEMBLY__
for its.S build") fixed the build error, but it should not have
defined __ASSEMBLY__ just for textual substitution in arbitrary data.
The file is image tree source in this case, but the purpose of using
CPP is to replace some macros.

I merged a better solution, commit a95b37e2 ("kbuild: get
<linux/compiler_types.h> out of <linux/kconfig.h>").  The original
fix-up is no longer needed.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Patchwork: https://patchwork.linux-mips.org/patch/19096/Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org

arch/mips/boot/Makefile

@@ -126,7 +126,6 @@ $(obj)/vmlinux.its.S: $(addprefix $(srctree)/arch/mips/$(PLATFORM)/,$(ITS_INPUTS
 
 quiet_cmd_cpp_its_S = ITS     $@
       cmd_cpp_its_S = $(CPP) $(cpp_flags) -P -C -o $@ $< \
-			-D__ASSEMBLY__ \
 		        -DKERNEL_NAME="\"Linux $(KERNELRELEASE)\"" \
 			-DVMLINUX_BINARY="\"$(3)\"" \
 			-DVMLINUX_COMPRESSION="\"$(2)\"" \