ramips: fix RBM33G partitioning

ramips: fix RBM33G partitioning

This patch improves 5684d087418d176cfdef4e045e1950ca7ba3b09f by correcting
the partition scheme for the "RouterBoot" section of the flash.

The partition scheme initially submitted is incorrect and does not reflect
the actual flash structure.

The "RouterBoot" section (name matching OEM) is subdivided in several
static segments, as they are on ar71xx RB devices albeit with different
offsets and sizes.
The naming convention from ar71xx has been preserved, except for the
bootloaders which are named "bootloader1" and "bootloader2" to avoid
confusion with the master "RouterBoot" partition.
The preferred 'fixed-partitions' DTS node syntax is used, with nesting
support as introduced in 2a598bbaa3.
"partition" is used for node names, with associated "label" to match
policy set by 6dd94c2781.

The OEM source code also define a "RouterBootFake" partition at the
beginning of the secondary flash chip: to avoid trouble if OEM ever makes
use of that space, it is also defined here.

The resulting partition scheme looks like this:
[   10.114241] m25p80 spi0.0: w25x40 (512 Kbytes)
[   10.118708] 1 fixed-partitions partitions found on MTD device spi0.0
[   10.125049] Creating 1 MTD partitions on "spi0.0":
[   10.129824] 0x000000000000-0x000000040000 : "RouterBoot"
[   10.136215] 5 fixed-partitions partitions found on MTD device RouterBoot
[   10.142894] Creating 5 MTD partitions on "RouterBoot":
[   10.148032] 0x000000000000-0x00000000f000 : "bootloader1"
[   10.154336] 0x00000000f000-0x000000010000 : "hard_config"
[   10.160665] 0x000000010000-0x00000001f000 : "bootloader2"
[   10.167046] 0x000000020000-0x000000021000 : "soft_config"
[   10.173461] 0x000000030000-0x000000031000 : "bios"
[   10.190191] m25p80 spi0.1: w25q128 (16384 Kbytes)
[   10.194950] 2 fixed-partitions partitions found on MTD device spi0.1
[   10.201271] Creating 2 MTD partitions on "spi0.1":
[   10.206071] 0x000000000000-0x000000040000 : "RouterBootFake"
[   10.212746] 0x000000040000-0x000001000000 : "firmware"
[   10.307216] 2 minor-fw partitions found on MTD device firmware
[   10.313044] 0x000000040000-0x000000220000 : "kernel"
[   10.319002] 0x000000220000-0x000001000000 : "rootfs"
[   10.324906] mtd: device 9 (rootfs) set to be root filesystem
[   10.330678] 1 squashfs-split partitions found on MTD device rootfs
[   10.336886] 0x000000b40000-0x000001000000 : "rootfs_data"

Leave a note in DTS to explain how the original author selected the SPI speed.

Tested-by: Tobias Schramm <tobleminer@gmail.com>
Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>
Reviewed-by: Rafał Miłecki <rafal@milecki.pl>
[rmilecki: dropped "RouterBootFake" partition]
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
(backported from b90cad2c2e61720b72a9cdd6317474cabc4962ec)