bsp/lpc24xx: Add lpc24xx_pin_get_first_index()
bsp/lpc24xx: Add LPC24XX_PIN_ETHERNET_POWER_DOWN
bsps/arm: Reset MII management in LPC Ethernet

Reduce MII clock to support LPC17XX.
bsps/arm: Add PHY detection to LPC Ethernet
bsps/arm: Add DP83848 PHY support to LPC Ethernet