USB: gadget: ethernet gadget cleanups, shrinkage

Clean up the ethernet gadget, using newer APIs and conventions:

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

 - Remove many now-needless #includes

 - Use the VERBOSE_DEBUG convention

 - Minor whitespace fixes.

 - Fix a warning from "sparse".

Surprisingly, this saved about 2K of code (16%) on a fullspeed-only
ARMv4 platform.  I'm bit puzzled by that (it's so much!), but approve
of the result.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>