net: Add device tree support to LPC32xx

This patch adds device tree support for lpc_eth.c.

The runtime option for MII/RMII is solved via the "phy-mode" property, SRAM
("IRAM") usage for DMA can be chosen via "use-iram".

Signed-off-by: Roland Stigge <stigge@antcom.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: David S. Miller <davem@davemloft.net>