m68k: Pass -D options to KBUILD_CPPFLAGS instead of KBUILD_{A,C}FLAGS

Precisely, -D is a preprocessor option.

KBUILD_CPPFLAGS is passed for compiling .c and .S files too.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Greg Ungerer <gerg@linux-m68k.org>
Link: https://lore.kernel.org/r/20200526123810.301667-4-masahiroy@kernel.org


Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>