arm64: dts: imx8mp: Drop i.MX8MP DHCOM rev.100 PHY address workaround from PDK3 DT

In case the i.MX8MP DHCOM rev.100 has been populated on the PDK3
carrier board, the on-SoM PHY PHYAD1 signal has been pulled high
by the carrier board and changed the PHY MDIO address from 5 to 7.
This has been fixed on production rev.200 SoM by additional buffer
on the SoM PHYAD/LED signals, remove the workaround.

Signed-off-by: Marek Vasut <marex@denx.de>