imx8mn-var-som: fix non-applied PHY reset-gpios properties

imx8mn-var-som: fix non-applied PHY reset-gpios properties

Select DM_ETH_PHY so that the reset-gpios property of the ethphy node
can be used.

Also select DM_PCA953X, which is needed for resetting the
ethernet PHY on the carrier board via the PCA9534 I/O expander.

Commit 4e5114daf9eb ("imx8mn: synchronise device tree with linux") did
synchronise device tree with linux, which in effect removed obsolete
PHY reset properties and replaced them with new mdio DM
properties. But the commit didn't activate DM_ETH_PHY or DM_PCA953X.

Fixes: 4e5114daf9eb ("imx8mn: synchronise device tree with linux")

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>