MLK-14513 ARM: imx: restore iomux/gpio settings before isoack on i.mx7ulp

MLK-14513 ARM: imx: restore iomux/gpio settings before isoack on i.mx7ulp

ISOACK must be done only after all IOMUX/GPIO settings done,
otherwise, some PADs can NOT keep state during VLLS
enter/exit and cause some pins toggling, and lead to
external devices in abnormal state, like reset etc..

This patch does all iomux/gpio settings restore in VLLS exit
flow, since DDR PADs need to be functioning before jump
to DDR, so isoack can only be done in ASM code, to save
OCRAM space, all pins in port C - F will be restored, even
some pins are reserved, but read/write these reserved pins
settings are OK on i.MX7ULP.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>