ipq40xx: fix second 5ghz radio on Netgear RBx40

ipq40xx: fix second 5ghz radio on Netgear RBx40

When support was added for the RBR40 and RBS40 it was assumed that they
also share the same second 5ghz wifi chip as their bigger siblings.
Turns out that instead of QCA9984 (RBx50, SRx60) these devices use
QCA9886 like the RBx20 devices to.
They also load different boardfiles for the IPQ4019 chip.

This moves the wifi nodes from the orbi.dtsi to each device dts file and
change the RBx40 boardfile variants.

Signed-off-by: Christoph Krapp <achterin@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/20877
Signed-off-by: Robert Marko <robimarko@gmail.com>