arm: mvebu: Define env_sf_get_env_addr() for all Armada boards in SPL

SPI0 CS0 Flash is mapped to address range 0xD4000000 - 0xD7FFFFFF by BootROM.
Proper U-Boot removes this direct mapping. So it is available only in SPL.
This applies for all 32-bit Armada BootROMs. SPL mvebu code is used only on
32-bit Armada SoCs. So move env_sf_get_env_addr() function from Turris
Omnia board to common SPL mvebu code and add proper checks for SPI0 CS0.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>