lpc_eth: remove obsolete ifdefs

The #ifdefs regarding CONFIG_ARCH_LPC32XX_MII_SUPPORT and
CONFIG_ARCH_LPC32XX_IRAM_FOR_NET are obsolete since the symbols have been
removed from Kconfig and replaced by devicetree based configuration.

Signed-off-by: Roland Stigge <stigge@antcom.de>
Signed-off-by: David S. Miller <davem@davemloft.net>