ppc4xx: (Re-)Enable CONFIG_PCI_PNP on AMCC 440EPx Sequoia

ppc4xx: (Re-)Enable CONFIG_PCI_PNP on AMCC 440EPx Sequoia

The 440EPx has a problem when the PCI_CACHE_LINE_SIZE register is
set to non-zero, because it doesn't support MRM (memory-read-
multiple) correctly. We now added the possibility to configure
this register in the board config file, so that the default value
of 8 can be overridden.

Here the details of this patch:

o drivers_pci_auto.c: introduce CFG_PCI_CACHE_LINE_SIZE to allow
  board-specific settings. As an example the sequoia board requires 0.
  Idea from Stefan Roese <sr@denx.de>.
o board/amcc/sequoia/init.S: add a TLB mapping at 0xE8000000 for the
  PCI IO-space. Obtained from Stefan Roese <sr@denx.de>.
o include/configs/sequoia.h: turn CONFIG_PCI_PNP back on and set
  CFG_PCI_CACHE_LINE_SIZE to 0.

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