PCI: read memory ranges out of Broadcom CNB20LE host bridge

Read the memory ranges behind the Broadcom CNB20LE host bridge out of the
hardware. This allows PCI hotplugging to work, since we know which memory
range to allocate PCI BAR's from.

The x86 PCI code automatically prefers the ACPI _CRS information when it is
available. In that case, this information is not used.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>