An i210 (aka e1000_igb) supports two different non-volatile storages for
configuration. There is a built-in one-time programmable storage called
iNVM and an optional external SPI-Flash. If a flash is populated and
contains a valid configuration image the iNVM is not used (if I
understood the documentation correctly). Still the iNVM can be useful if
the flash is not configured. Also the iNVM contains manufacturing
identification information.

So it makes sense to provide the invm device even if a flash is present.

This patch also cleans up some confusion that suggests that invm is a
way to access the (simulated) eeprom structures and drops some unused
enum values.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>