I noticed that musb is blocking core retention for omap4 unlike for
omap3. This is because for omap3 we have phy-twl4030-usb implement
it's own PM runtime to handle errata "VUSB3V1 VBUS overvoltage
debouncer not working when the PHY is powered down". That is done
in order to keep the USB PHY powered when phy-twl4030-usb is loaded.

For the other USB PHYs, we need to enable and disable the PHY based on
musb PM runtime. With the session bit based PM runtime for musb core,
we can now idle the USB PHY always when musb is idle.

Note that adding these calls will not affect the twl4030 driver
as it's phy functions will just query the PHY state without powering
the PHY on or off.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>