MLK-17290-05 gpio: mxc: save and restore gpio controller registers when power off

MLK-17290-05 gpio: mxc: save and restore gpio controller registers when power off

Save gpio controller registers before power off, and then restore these
registers after power on. There have two cases need to save/restore regs:
  a. If sub_irqs/sub_gpios are not free/released, device suspend() force
     runtime suspend and power domain off in suspended stage, it needs to
     keep the previous registers value after device resume back.
  b. If some sub_irqs set irq type just one time, then irqchip should restore
     the registers for correct irq type.

Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Tested-by: Guoniu.Zhou <guoniu.zhou@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>