ARM: imx8ulp: support env in fat and ext4

ARM: imx8ulp: support env in fat and ext4

Change boot device logic to also allow environment stored in fat and
in ext4 when booting from SD or eMMC.

As the boot device check for SD and for eMMC was depending on
ENV_IS_IN_MMC being defined, change the ifdef blocks at
env_get_location to use IS_ENABLED instead for all modes, returning
NOWHERE when no valid mode is found.

Signed-off-by: Ricardo Salveti <ricardo@foundries.io>
Co-developed-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>