lib: utils/timer: Add FDT based ACLINT MTIMER driver

We add a new FDT based ACLINT MTIMER driver which works for
both CLINT device and standalone ACLINT MTIMER device.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Xiang W <wxjstz@126.com>