lib: utils/reset: Add syscon based reboot and poweroff

Let us have common FDT based reset driver for syscon reboot and
poweroff. The device tree bindings for syscon reboot and poweroff
are already available in the Linux kernel sources.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>