fsl_usb2_udc: Fix some sparse warnings and remove redundant code.

Fix some sparse "integer used as NULL pointer" warnings.
Remove some unnecessary volatiles and static initialization.
Remove some unused struct members and reorder to improve packing.
Remove a few unneeded includes.

Signed-off-by: Will Newton <will.newton@gmail.com>
Acked-by: Li Yang <leoli@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>