[mv_pci] Increase default PCI space size for mv_pci
mv_pci driver reads PCI memory window layout from DTB data and if the
data is incomplete falls back to default value. The value is too small
to fit two PCI spaces for mwlwifi devices on WRT3200ACM so the resource
allocation for them fails. Increase the default to 4Mb from 1Mb so
the devices can be properly attached.
MFC after: 1 week