ARM: UniPhier: include PH1-LD4 Makefile from PH1-sLD8

The two Makefiles arch/arm/mach-uniphier/{ph1-ld4,ph1-sld8}/Makefile
are completely the same.  We can improve the maintainability by
having one to include the other.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>