Add power down/restart related below API
 - Force power down
 - System shutdown
Signed-off-by: Tejas Patel <tejas.patel@xilinx.com>
Signed-off-by: Jolly Shah <jolly.shah@xilinx.com>
Change-Id: Icd4a922923b1fd50eca1f5361f1e604aedcdb529