[POWERPC] 4xx: Add AMCC Glacier 460GT eval board dts

The patch adds the Glacier dts. The Glacier is nearly identical to the
Canyonlands (460EX). Here the differences:

- 4 ethernet ports instead of 2
- no SATA port
- no USB port

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