On systems with PIO3 (SAMA5D3/D4/..), the pullup and pulldown configuration
is mutualy exclusive. This patch assures that the opposite pull resistor gets
disabled before the requested pull resistor is enabled. This changes behavior
of at91_set_pio_pulldown() such that the pullup is only disabled if pulldown
is to be enabled. This changes behavior of at91_set_pio_pullup() such that
the pulldown is only disabled if pullup is to be enabled.