move OMAP's transceiver glue to drivers/usb/otg

Move otg_get/set/put_transceiver() from omap specific code
to common otg.c so other upcoming drivers can share them.

[ dbrownell@users.sourceforge.net: move to drivers/usb/otg, dox ]

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Felipe Balbi <me@felipebalbi.com>
Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>