make the wwan driver listen to 4G_WAKE and wake the system

even in mainline we currently describe the 4G_WAKE pin as gpio-key for the devkit: https://elixir.bootlin.com/linux/latest/source/arch/arm64/boot/dts/freescale/imx8mq-librem5-devkit.dts#L53 and we want to do the same for the phone.

but that looks like a short-term workaround: the KEY_PHONE describes a physical key that starts a phone application (afaik). This is not what's happening here and not what we have on the phone (or devkit).

so the wwan driver should look at this pin and wake the system on incoming calls and sms instead, right?