[POWERPC] 4xx: Add TAH support to taishan dts

This patch adds TAH (TCP/IP Acceleration Hardware) support to the
taishan 440GX dts. It depends on the NEWEMAC/tah patch that adds the
compatible "ibm,tah" property to the matching table.

Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>