net: ethtool: Add ethernet speed macros for higher speeds

Add speed macro's for higher ethernet speeds to be used in u-boot
networking drivers. Added Macros for speeds 14G, 20G, 25G, 40G, 50G,
56G, 100G and 200G inline with linux.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>