ARM: imx: Reinstate decode ECSPI env location from i.MX8M ROMAPI tables

Decode ECSPI boot device in env_get_location() from i.MX8M ROMAPI tables.
This is necessary to correctly identify env is in SPI NOR when the system
boots from SPI NOR attached to ECSPI.

This reinstates change from commit:
e26d0152 ("ARM: imx: Decode ECSPI env location from i.MX8M ROMAPI tables")
which has been dropped in commit:
b0a284a7 ("imx: move get_boot_device to common file")

Fixes: b0a284a7 ("imx: move get_boot_device to common file")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>