EHCI: update PM methods in ehci-tegra.c

This patch (as1547) rearranges the Power Management parts of the
ehci-tegra driver to match the conventions used in other EHCI platform
drivers.  In particular, the controller should not be powered down by
the root hub's suspend routine; the controller's power level should be
managed by the controller's own PM methods.

The end result of the patch is that the standard ehci_bus_suspend()
and ehci_bus_resume() methods can be used instead of special-purpose
routines.  The driver now uses the standard dev_pm_ops methods instead
of legacy power management.  Since there is no supported wakeup
mechanism for the controller, runtime suspend is forbidden by default
(this can be overridden via sysfs, if desired).

These adjustments are needed in order to make ehci-tegra compatible
with recent changes to the USB core.  The core now checks the root
hub's status following bus suspend; if the controller is automatically
powered down during bus suspend then the check will fail and the root
hub will be resumed immediately.  Doing the controller power-down in a
separate method avoids this problem.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>