colibri-imx6ull: specify MTD partitions on command line

Disable fdt_fixup_mtdparts() and pass MTD partition on the command
line. Dynamically editing the fdt with a static partitions configuration
is not required and there is no advantages compared to using the command
line. This change should prevent boot failures as the one in [0].

Cc: Marek Vasut <marex@denx.de>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/all/Y4dgBTGNWpM6SQXI@francesco-nb.int.toradex.com/ [0]
Link: https://lore.kernel.org/all/20230105123334.7f90c289@xps-13/


Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Link: https://lore.kernel.org/all/20230206224838.75963-4-francesco@dolcini.it/


Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>