USB: atmel_usba_udc: change way of specifying bias function

The toggle_bias() function was specified differently for avr32 and at91
architectures. Now, new at91 have the same behavior as avr32.
Consequently, we change to a particular chip function definition: only for
at91sam9rl.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>