[POWERPC] cuboot-pq2: PCI fixes

1. Detect (and bail out on) more conditions that violate the
assumptions of the setup code -- we assume in such cases that the device
tree is correct and reflects what the firmware did.

2. The inbound memory mask calculation was wrong.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>