sh: Move build rule for cchips/hd6446x/ to arch/sh/Kbuild

This is the last user of core-y in arch/sh.

Use the standard obj-y syntax.

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/20230219141555.2308306-2-masahiroy@kernel.org


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