dt-bindings: mtd: partitions: add TP-Link SafeLoader layout

Most TP-Link home routers use the same partitioning system based on a
custom ASCII table.

It doesn't seem to have any official name. GPL sources contain tool
named simply "make_flash" and Makefile target "FlashMaker".

This partitions table format was first found in devices with a custom
SafeLoader bootloader so it was called SafeLoader by a community. Later
it was ported to other bootloaders but it seems the name sticked.

Add binding for describing flashes with SafeLoader partitions table. It
allows operating systems to parse it properly and register proper flash
layout.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20221015092950.27467-1-zajec5@gmail.com