arm: mvebu: Remove redundant u-boot, dm-pre-reloc from all 32-bit Armada SoCs

Replace it by including of mvebu-u-boot.dtsi file. When board does not use
-u-boot.dtsi then mvebu-u-boot.dtsi is included automatically by makefile
scripts/Makefile.lib.

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