stm32mp1: Update env_get_location for NOR support

stm32mp1: Update env_get_location for NOR support

Update env_get_location() to be able to save environment into
NOR (SPI_FLASH).

Series-cc: pde, cke, pch, uboot-stm32

Cover-letter:
Add saveenv support for STM32MP1

This series adds saveenv support for STM32MP1 on several boot
devices. STM32MP1 is able to boot on eMMC, sdcard and NOR
(NAND support is not fully supported).

On eMMC and sdcard, environment is saved in EXT4 partition
On NOR, environment is saved in a dedicated partition
On NAND, environment is saved in a UBI volume.

This series:
  - enables NAND and NOR support on ev1 board
  - enables ENV_IS_IN_SPI_FLASH, ENV_IS_IN_UBI, ENV_IS_IN_EXT4
    flags
  - fixes get_mtdparts()
  - allows to override interface, device and partition for ext4
    environment
  - updates rule to set ENV_IS_NOWHERE value
  - introduce ENV_IS_IN_DEVICE
END

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>