staging: et131x: Tidy up PCI device table definition

Used the convenience macros DEFINE_PCI_DEVICE_TABLE and PCI_VDEVICE to
tidy up the device table definition.

Also remove the corresponding TODO item from the README.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>