arm: mvebu: AC5/AC5X: Disable SMBIOS

The RD-AC5X doesn't make use of EFI or SMBIOS. Recently we started seeing
boot failures such as

    WARNING: SMBIOS table_address overflow 27f60f020
    Failed to write SMBIOS table
    initcall failed at event 10/(unknown) (err=-22)
    ### ERROR ### Please RESET the board ###

The error is because the physical address of the RAM on the AC5X SoC is
above the 32GiB boundary. As we don't need SMBIOS or EFI this can be
safely disabled.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>