sh: Remove compiler flag duplication

Every compiler flag added by arch/sh/Makefile is passed to the
compiler twice:

$(KBUILD_CPPFLAGS) + $(KBUILD_CFLAGS) is used for compiling *.c
$(KBUILD_CPPFLAGS) + $(KBUILD_AFLAGS) is used for compiling *.S

Given the above, adding $(cflags-y) to all of KBUILD_{CPP/C/A}FLAGS
ends up with duplication.

Add -I options to $(KBUILD_CPPFLAGS), and the rest of $(cflags-y)
to KBUILD_{C,A}FLAGS.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/20230219141555.2308306-4-masahiroy@kernel.org


Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>