[POWERPC] 4xx: Fix PCI mem in sequoia DTS

This patch is fixes the sequoia.dts device tree file to use the values defined
in the 440Epx data sheet from AMCC.

That fixes an issue where some devices, including graphics cards, would not
initialize properly because the PCI resource space was not big enough.

Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>