linux-imx

MLK-21900-2 usb: chipidea: imx: turn off vbus comparator when suspend

As we use bvalid for vbus wakeup source, to save power when
suspend, turn off the vbus comparator for imx7d and imx8mm.

Below is this bit description from RM of iMX8MM
"VBUS Valid Comparator Enable:
 This signal controls the USB OTG PHY VBUS Valid comparator which
indicates whether the voltage on the USB_OTG*_VBUS pin is below
the VBUS Valid threshold. The VBUS Valid threshold is nominally
4.75V on this USB PHY. The VBUS Valid threshold can be adjusted
using the USBNC_OTGn_PHY_CFG1[OTGTUNE0] bit field. Status of the
VBUS Valid comparator, when it is enabled, is reported on the
USBNC_OTGn_PHY_STATUS[VBUS_VLD] bit.
When OTGDISABLE0 (USBNC_USB_OTGx_PHY_CFG2[10])is set to 1'b0 and
DRVVBUS0 is set to 1'b1, the Bandgap circuitry and VBUS Valid
comparator are powered, even in Suspend or Sleep mode.
DRVVBUS0 should be reset to 1'b0 when the internal VBUS Valid comparator
is not required, to reduce quiescent current in Suspend or Sleep mode.
 - 0 The VBUS Valid comparator is disabled
  - 1 The VBUS Valid comparator is enabled"

Signed-off-by: Li Jun <jun.li@nxp.com>