usb: phy: am335x: Enable USB remote wakeup using PHY wakeup

USB remote wakeup using PHY wakeup is supported only in standby mode.
Enabling the PHY_WKUP will break DS0 mode of system suspend.
If the same is enabled while entering DS0, AM33xx never stays in DS0,
it returns immediately from DS0. By default make the PHY wakeup
disabled, using sysfs entry enable the same manually to get
the remote wakeup working from standby.

echo enabled > /sys/bus/platform/device/<usb phy id>/power/wakeup
This will enable the PHY wakeup while going to standby.

PHY wakeup feature is required to wakeup  the system from standby
state. Since AM33xx has a bug in which PHY wakeup should not
be enabled while entering DS0, disable the same by default.
A user wishing to use USB wakeup from standby mode need to enable
the same using the sysfs entries.

Also remove am335x_phy_runtime_(suspend/resume) this driver doesnot really
enable/disable the clocks to the PHY.
Add am335x_phy_(suspend/resume) and use the same for enabling the PHY_WKUP.

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>