qualcommax: ipq8074-ess: move switch to ess-instance node

qualcommax: ipq8074-ess: move switch to ess-instance node

It seems that newer SSDK is now expecting the switch node to be a subnode
of "ess-instance" node which also contains "num_devices" as the number of
switches as you can also have external switches connected.

Asus RT-AX89X is even more peculiar as its bootloader has a hardcoded path
to enable if on that revision there is an AQR113 connected to port 6 of the
switch.

So, lets move the current switch node under ess-instance as otherwise it
seems that SSDK is having some issues parsing the UNIPHY mode properly as
I am getting the following:
[    6.981404] _adpt_hppe_instance1_mode_get[3275]:ERROR:port 6 doesn't support port_interface_mode 9

Which should not happen as that port has the mode set to 13.

Link: https://github.com/openwrt/openwrt/pull/15840
Signed-off-by: Robert Marko <robimarko@gmail.com>