The actual layout for OCELOT_GPIO_ALT[01] when there are more than 32 pins
is interleaved, i.e. OCELOT_GPIO_ALT0[0], OCELOT_GPIO_ALT1[0],
OCELOT_GPIO_ALT0[1], OCELOT_GPIO_ALT1[1]. Introduce a new REG_ALT macro to
facilitate the register offset calculation and use it where necessary.