arm64: dts: imx8mp: Do not delete PHY nodes on i.MX8MP DHCOM PDK2

The PHY nodes may be activated via DTO in case another SoM variant
is populated into the development kit. Do not delete the nodes.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>