arm64: dts: ti: k3-j721s2: Enable WKUP_GPIO6 for SW3.1

SW3.1 is a physical switch muxing between OSPI NOR and OSPI NAND.
SW3.1 is connected to the wkup_gpio0_6 pin. Enable the support for
wkup_gpio0_6 for adding OSPI dual flash support.

Signed-off-by: Prasanth Babu Mantena <p-mantena@ti.com>