[POWERPC] Add support for PORTA and PORTB odr registers

PORTA and PORTB have odr registers, as well. However, the PORTB odr
register is only 16bit.

Signed-off-by: Jochen Friedrich <jochen@scram.de>
Acked-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Vitaly Bordug <vitb@kernel.crashing.org>