Non volatile device variables are used to make device parameters
persistent. They are like normal non volatile variables, but set
the values of the device parameters with the corresponding name.
Every nv variable beginning with nv.dev is a non volatile device
variable. They have the form nv.dev.<devname>.<paramname> and act
on the parameter <paramname> of the device named <devname>.

The non volatile device variables are designated for example for
video modes, ethernet device ip addresses or mtd partitioning.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>