Drop in mdev.conf and the /lib/mdev/persistent-storage script, these
cause /dev/disk/by-* to be populated in the ramdisk, making it
possible to do look up partition by-label and by-partlabel for free,
compared to findfs which can take some time.
As a first optimisation based on this, check for some partitions using
these paths and prioritise them when looking for subpartitions. Drop the
first find_boot_partition call as it doesn't really save time over the
call in the while loop.
The mdev config also handles setting up /dev/null, /dev/random, etc, so
these don't have to be done manually.
