kernel: mtd: parsers: add nvmem support to cmdlinepart

kernel: mtd: parsers: add nvmem support to cmdlinepart

Assuming cmdlinepart is only one level deep partition scheme and that
static partition are also defined in DTS, we can assign an of_node for
partition declared from bootargs.

The cmdlinepart parser is the first parser checked and if it does find
some partition declared in the bootargs, every other parser is ignored.
This means that the fixed-partition parser is ignored and an of_node for
the mtd is never assigned.
Fix this by searching a defined of_node using a similar fixed_partition
parsing logig, check if a partition is present with the same label, check
that it has the same offset and size and finally assign an of_node to the
mtd. The NVMEM can now find the of_node for the mtd and correctly works.

Fixes: abc17bf306ac ("ath79: convert mtd-mac-address to nvmem implementation")
Tested-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>