Commit 0a672d49 "arm: Add Prep subcommand support to bootm" re-organized
do_bootm_linux for ARM. During the re-organization, the call to
fdt_fixup_ethernet() was removed. I assume this was useful, so add it
back.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Tom Rini <trini@ti.com>