ARM: uniphier: revive accidentally removed dcache_disable()

Commit a8e6300d483d ("ARM: uniphier: refactor spl_init_board()")
accidentally dropped dcache_disable() call.  Since then, the SPL of
LD11 and LD20 failed to load U-Boot proper.

Fixes: a8e6300d483d ("ARM: uniphier: refactor spl_init_board()")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/arm/mach-uniphier/spl_board_init.c

@@ -168,4 +168,8 @@ void spl_board_init(void)
 		pr_err("failed to init DRAM\n");
 		hang();
 	}
+
+#ifdef CONFIG_ARM64
+	dcache_disable();
+#endif
 }