arm64: dts: ti: k3-am642-evm: Add USB support

AM64 EVM board has a micro USB 2.0 AB connector and the USB0_VBUS is
connected with a resistor divider in between. USB0_DRVVBUS pin is muxed
between USB0_DRVVBUS and GPIO1_79 signals.

Add the corresponding properties and set the pinmux mode for USB subsystem
in the evm dts file.

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Acked-by: Roger Quadros <rogerq@ti.com>