twl4030-usb updates/fixes

Simplify handling of VBUS and ID status and the USB_PRES interrupt.
This seems to resolve the problems I previously saw on Beagle and
Overo boards.

 - Read the status directly, instead of trying to infer it from
   dodgey side effects of IRQ handling and trigger tweaking.

 - Stop trying to arrange those dodgey side effects; just leave
   the IRQ enabled at all times.

 - Check that status as part of driver probe, so the PHY can
   always be active by the time it's needed.  (BUGFIX!)

 - Re-sequence probe() to be less racey, and to avoid duplicating
   logic found elsewhere (notably irq handling and PHY activation).

 - Make the irq_chip be the exclusive owner of PWR_EDR (finally).

 - Get rid of needless work_struct ... in this irq handling thread,
   it's safe and cheap to call sysfs_notify() directly.

Stop enabling IRQs on the USB subchip.  There's no IRQ handler for
them, and since ALT_INT_REROUTE isn't being set they'll never
arrive ... so there's no point to enabling them.

Also add some comments about other things such an otg_transciever
driver should be doing, fixing minor omissions; and remove some
unnecessary file inclusions.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>