ramips: convert most mtd-mac-address cases in DTSI to nvmem

ramips: convert most mtd-mac-address cases in DTSI to nvmem

Convert most of the cases from mtd-mac-address to nvmem where
MAC addresses are set in the DTSI, but the partitions are only
located in the device DTS. This posed some problems earlier, since
in these cases we are using partitions before they are defined,
and the nvmem system did not seem to like that.

There have been a few different resolution approaches, based on
the different tradeoffs of deduplication vs. maintainability:

 1. In many cases, the partition tables were identical except for
    the firmware partition size, and the firmware partition was
    the last in the table.
    In these cases, the partition table has been moved to the
    DTSI, and only the firmware partition's "reg" property has
    been kept in the DTS files. So, the updated nvmem definition
    could stay in the DTSI files as well.

 2. For all other cases, splitting up the partition table would
    have introduced additional complexity. Thus, the nodes to be
    converted to nvmem have been moved to the DTS files where the
    partitioning was defined.

 3. For Netgear EX2700 and WN3000RP v3, the remaining DTSI file
    was completely dissolved, as it was quite small and the name
    was not really nice either.

 4. The D-Link DIR-853 A3 was converted to nvmem as well, though
    it is just a plain DTS file not taken care of in the first
    wave.

In addition, some minor rearrangements have been made for tidyness.

Not covered (yet) by this patch are:

 * Various unielec devices
 * The D-Link DIR-8xx family

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>