Add more host/OTG functionality.

New Features:
   -	Cable based role switching (using the ID pin) mostly works.  This gives
	much of the end-user value for USB OTG; there's also dynamic role
	switching (using special HNP protocol with another OTG device), which
	surely won't work yet.
   -	Root can write 0/N to /sys/module/musb_hdrc/parameters/musb_otg to
   	disable OTG functionality, forcing B-Default mode (with optional SRP
	support, but without 8mA current limits) when it's set.  Change this
	before the gadget driver initializes (e.g. before "modprobe").

Bugfixes:
   -	Fix many OTG mode startup glitches, notably for the root hub.
   -	Add workaround for "issue 4".

Cleanups:
   -	Remove more mode-specific #ifdeffery
   -	ReMoveSomeCamelCasing
   -	Quieter startup
   -	Quash another Kconfig rebellion
   -	Add missing bit declaration
   -	Tersify TUSB irq messages

Open Issues:
   -	Nothing passes remote wakeup down to root hub (unchanged)
   -	Strange VBUS errors (unchanged; workaround: use hub modified for
	N770, providing 5V supply till TUSB board does so reliably);
   -	Plug in/out as peripheral many times; fine.  As host (with modified
	hub), ditto.  Now peripheral again ... fails.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>