ppc4xx: Add PCIe endpoint support on Kilauea (405EX)

This patch adds endpoint support for the AMCC Kilauea eval board. It can
be tested by connecting a reworked PCIe cable (only 1x lane singles
connected) to another root-complex.

In this test setup, a 64MB inbound window is configured at BAR0 which maps
to 0 on the PLB side. So accessing this BAR0 from the root-complex will
access the first 64MB of the SDRAM on the PPC side.

Signed-off-by: Stefan Roese <sr@denx.de>