[POWERPC] 86xx: mpc8610_hpcd: add support for PCI Express x8 slot

This patch adds pcie node which is resposible for PCI-E x8 slot
functioning. Though, this was tested using only x1 SKY2 NIC.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>