MUSB: Miscellaneous updates

Lots of miscellaneous updates:

  - bugfixes
     * flag hcd-framework "got irq" state earlier
     * reject urb submission if port is suspended
     * linkage fix: unbind became optional
     * initialize vbus error retry count earlier
     * tusb init removes diagnostic-only settings
  - procfs updates
     * always show otg state info in procfs
     * show some TUSB-specific registers in procfs
  - cleanups
     * remove pointless MUSB_ERR stuff (handled better now)
     * tusb init removes dead code
     * more informative vbus error debug message
     * comment fixes
     * etc

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