net: sh_eth: Support reset GPIO both in mac and phy node

The recent DTs have the PHY reset GPIO in the PHY node rather than
the ethernet MAC node, support extracting the PHY reset GPIO info
from both the PHY node and ethernet MAC node.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Cc: Joe Hershberger <joe.hershberger@ni.com>