arm: mvebu: Espressobin: Setup MTD partitions when booting kernel

Due to different partition layouts in different U-Boot versions, DTS for
Espressobin in Linux does not contain any definition of MTD partitions.
See commit https://git.kernel.org/stable/c/00954566464a4

 for more details.

This patch via ft_board_setup() hook fills current partition layout used by
U-Boot, so booted kernel would see correct MTD partitions layout.

U-Boot env partition is calculated from CONFIG_ENV_OFFSET option.

First partition contains secure firmware, ARM trusted firmware and U-Boot
with checksums. So it is not possible to replace just one image (e.g.
U-Boot) without updating other parts where is stored checksum of U-Boot.
Therefore there is no extra partition defined for U-Boot and first
partition is called just 'firmware'.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Konstantin Porotchkin <kostap@marvell.com>
Tested-by: Andre Heider <a.heider@gmail.com>