Adds a test using a makeshift MDIO MUX. The test is based on the existing
MDIO test. It uses the last emulated PHY register to verify MUX selection.
Signed-off-by: Alex Marginean <alexm.osslist@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
