arm64: dts: ti: k3-j721e-mcu: add scm node and phy-gmii-sel nodes

Add DT node for MCU System Control module DT node and DT node for the TI
J721E SoC phy-gmii-sel PHY required for Ethernet ports mode selection.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>