net: gem: Disable broadcast setting

There is no need for GEM to accepts broadcast packets because they are not
handled by u-boot anyway. That's why use HW IP feature and don't waste time
on these packats which will be dropped anyway.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Link: https://lore.kernel.org/r/0e236c3a6514a2a633ef3a5b71a967c46f7fbae7.1634303007.git.michal.simek@xilinx.com