Create menu entry to select device creation method

Four methods for the creation of device files in /dev are now
proposed:

 - static method uses device table as before
 - devtmpfs method enables this feature in kernel
 - mdev method adds mdev starting script to the file system
    and selects mdev itself for installation
 - udev method selects udev for installation

All dynamic methods are based on devtmpfs, so one doesn't need to care
about /dev folder.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>