arm64: dts: ti: k3-am642: reserve gpio in mcu domain for firmware usage

The gpio0 subsystem present in MCU domain might be used by firmware and is
not pinned out in evm/sk. Therefore, reserve it for MCU firmware.

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210319051950.17549-3-a-govindraju@ti.com