Plasma - most MIPS I(TM) opcodes

PAR comnplained bitterly and insisted that I add the CLOCK_DEDICATED_ROUTE = FALSE constraint to the NET "E_RX_CLK" statement in spartan3e.ucf. After I did that, PAR succeeded.

I am using ISE 11.1

I simplified eth_dma.vhd to not use E_RX_CLK as a clock.