arm64: dts: ti: k3-j7200-mcu-wakeup: Enable ADC support

J7200 has a single instance of 8 channel ADC in MCU domain. Add DT node
for the same.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Sekhar Nori <nsekhar@ti.com>
Link: https://lore.kernel.org/r/20201029050950.4500-1-vigneshr@ti.com