USB: gadget: file storage gadget cleanups

Clean up the file storage gadget, using newer APIs and conventions:

 - gadget_is_dualspeed() and gadget_is_otg() ... #ifdef removal

 - Remove many now-needless #includes

 - Use the DEBUG (from Kconfig+Makefile) and VERBOSE_DEBUG conventions.

 - Remove some "sparse" warnings (it still dislikes the __user annotations)

This gave only a minor object code shrinkage.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>