arm64: dts: rockchip: add rfkill node for M.2 Key E WiFi on rock-5b

arm64: dts: rockchip: add rfkill node for M.2 Key E WiFi on rock-5b

By default the GPIO pin that connects to the WiFi enable signal
inside the M.2 Key E slot is driven low, resulting in impossibility
to connect to any network. Add a DT node to expose it as an RFKILL
device, which lets the WiFi driver or userspace toggle it as
required.

Signed-off-by: Alexey Charkov <alchark@gmail.com>
Link: https://lore.kernel.org/r/20240106202650.22310-1-alchark@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>