arm: mvebu: Fix Espressobin build for configs where ENV is not in SPI

arm: mvebu: Fix Espressobin build for configs where ENV is not in SPI

When storing the UBoot Environment in for example EXT4,
the U-Boot build is broken for several reasons:
1. armada-385-turris-omnia-u-boot.dtsi will not allow
   CONFIG_ENV_OFFSET and CONFIG_ENV_SIZE to be undefined
2. armada-37xx/board.c ft_board_setup function does not
   exist if CONFIG_ENV_IS_IN_SPI_FLASH is not defined

This commit changes these files so that selecting a
different location for the environment is possible.

Signed-off-by: Rogier Stam <rogier@unrailed.org>
Reviewed-by: Pali Rohár <pali@kernel.org>