generic: routerbootpart MTD parser for RouterBoot

generic: routerbootpart MTD parser for RouterBoot

This driver provides an OF MTD parser to properly assign the RouterBoot
partitions on the flash. This parser builds from the "fixed-partitions"
one (see ofpart.c), but it can handle dynamic partitions as found on
routerboot devices.

The parent node must contain the following:
	compatible = "mikrotik,routerboot-partitions";
	#address-cells = <1>;
	#size-cells = <1>;

Children routerbootpart DTS nodes are defined as follows:
For fixed partitions
	node-name@unit-address {
		reg = <prop-encoded-array>;
		label = <string>;
		read-only;
		lock;
	};

All properties but reg are optional.

For dynamic partitions:
	node-name {
		size = <prop-encoded-array>;
		label = <string>;
		read-only;
		lock;
	};

size property is mandatory unless the next partition is a fixed one or
a "well-known" one (matched from the strings defined below) in which case
it can be omitted or set to 0; other properties are optional.

By default dynamic partitions are appended after the preceding one, except
for "well-known" ones which are automatically located on flash.

Well-known partitions (matched via label or node-name):
 - "hard_config"
 - "soft_config"
 - "dtb_config"

This parser requires the DTS to list partitions in ascending order as
expected on the MTD device.

This parser has been successfully tested on BE (ath79) and LE (ipq40xx
and ramips) hardware.

Tested-by: Baptiste Jonglez <git@bitsofnetworks.org>
Tested-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>
Tested-by: Tobias Schramm <t.schramm@manjaro.org>
Tested-by: Christopher Hill <ch6574@gmail.com>
Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>