[netdrvr] Remove Becker-template 'io_size' member, when invariant
Becker-derived drivers often have the 'io_size' member in their chip
info struct, indicating the minimum required size of the I/O resource
(usually a PCI BAR). For many situations, this number is either
constant or irrelevant (due to pci_iomap convenience behavior).
This change removes the io_size invariant member, and replaces it with a
compile-time constant.