MLK-9674-3 arm: imx: add QSPI save/restore when M4 is enabled

As M4 is executing on QSPI2 flash, and QSPI is inside Mega/Fast
domain which may lost power in DSM, so we need to do save/restore
of QSPI2 controller to make sure QSPI flash can be accessed before
waking up M4 after exiting from DSM.

Signed-off-by: Allen Xu <b45815@freescale.com>
Signed-off-by: Anson Huang <b20788@freescale.com>