ARC: [plat-hsdk]: Switch ethernet phy-mode to rgmii-id

HSDK board has Micrel KSZ9031, recent commit
bcf3440c ("net: phy: micrel: add phy-mode support for the KSZ9031 PHY")
caused a breakdown of Ethernet.
Using 'phy-mode = "rgmii"' is not correct because accodring RGMII
specification it is necessary to have delay on RX (PHY to MAX)
which is not generated in case of "rgmii".
Using "rgmii-id" adds necessary delay and solves the issue.

Also adding name of PHY placed on HSDK board.

Signed-off-by: Evgeniy Didin <Evgeniy.Didin@synopsys.com>
Cc: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>