musb_hdrc misc cleanups

Remove debug/prototype sysfs attribute 'musb_otg', so there's only
the one (compound) state machine to follow.  (If we need an option
it'd more likely be to match the N800:  Mini-B connector forced
into host mode, with gender-bender assistance.)

Minor DaVinci tweak:  on driver shutdown, don't wait for VBUS to fall
unless we're the host which was supplying that voltage.

Remove some more UglyCamelCasing.

Clear HR in some peripheral side code; the silicon doesn't clear it
in various cases you'd expect such stuff to be automatic.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>