arm: delete unused macro CONFIG_ARCH_DEVICE_TREE

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Tom Warren <twarren@nvidia.com>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Rajeshwari Birje <rajeshwari.s@samsung.com>
Cc: Inderpal Singh <inderpal.singh@linaro.org>