MLK-12443 ARM: imx: disable low power mode before entering LPSR mode

MLK-12443 ARM: imx: disable low power mode before entering LPSR mode

Before entering LPSR mode, as GPC was set to STOP/DSM mode already,
the wfi loop after LPSR mode would cause system enter STOP/DSM mode
first, then SNVS will force PMIC_ON_REQ to low, as SNVS needs IPG
clock to be on before entering SNVS/LPSR mode, so we have to disable
STOP/DSM mode to make sure IPG clock is on before SNVS actually enters
LPSR mode.

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