ARM: dts: lpc18xx: configure dwmac properly

Configure the DWMAC FIFO sizes, burst length and threshold DMA mode on
LPC18xx/43xx SoCs. These parameters are needed for correct operation of
the Ethernet MAC. The DWMAC on LPC18xx/43xx does not support RSF DMA
mode and therefore must use threshold mode.
Signed-off-by: Joachim Eastwood <manabian@gmail.com>

arch/arm/boot/dts/lpc18xx.dtsi

@@ -186,6 +186,10 @@ mac: ethernet@40010000 {
 			clock-names = "stmmaceth";
 			resets = <&rgu 22>;
 			reset-names = "stmmaceth";
+			rx-fifo-depth = <256>;
+			tx-fifo-depth = <256>;
+			snps,pbl = <4>; /* 32 (8x mode) */
+			snps,force_thresh_dma_mode;
 			status = "disabled";
 		};