[POWERPC] 4xx: Add 440SPe revA runtime detection to PCIe

This patch adds runtime detection of the 440SPe revision A chips. These
chips are equipped with a slighly different PCIe core and need special/
different initialization. The compatible node is changed to
"plb-pciex-440spe" ("A" and "B" dropped). This is needed for boards that
can be equipped with both PPC revisions like the AMCC Yucca.

Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>