The GEMGXL_RST line on HiFive Unleashed is pulled low and is
using GPIO number 12. Add these reset-gpio details to dt-node
using which the linux phylib can reset the phy.
Signed-off-by: NSagar Shrikant Kadam <sagar.kadam@sifive.com>
Signed-off-by: NPalmer Dabbelt <palmerdabbelt@google.com>