ARM: uniphier: split ft_board_setup() out to a separate file

Prepare to add more fdt fixup code.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 376851e..dc9e24d 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1223,6 +1223,7 @@
 	select DM_RESET
 	select DM_SERIAL
 	select DM_USB
+	select OF_BOARD_SETUP
 	select OF_CONTROL
 	select OF_LIBFDT
 	select PINCTRL