net: lan969x: fix cyclic dependency reported by depmod

Depmod reports a cyclic dependency between modules sparx5-switch.ko and
lan969x-switch.ko:

depmod: ERROR: Cycle detected: lan969x_switch -> sparx5_switch -> lan969x_switch
depmod: ERROR: Found 2 modules in dependency cycles!
make[2]: *** [scripts/Makefile.modinst:132: depmod] Error 1
make: *** [Makefile:224: __sub-make] Error 2

This makes sense, as they both require symbols from each other.

Fix this by compiling lan969x support into the sparx5-switch.ko module.
In order to do this, in a sensible way, we move the lan969x/ dir into
the sparx5/ dir and do some code cleanup of code that is no longer
required.

After this patch, depmod will no longer complain, as lan969x support is
compiled into the sparx5-swicth.ko module, and can no longer be compiled
as a standalone module.

Fixes: 98a01119 ("net: sparx5: add compatible string for lan969x")
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>