mips: mscc: luton+ocelot: Remove board config options, do probing

mips: mscc: luton+ocelot: Remove board config options, do probing

As we are moving to multi-dtb and board detection, remove static board
config options, and introduce board probing instead.

Luton: This add single-binary support for the two MSCC luton-based
reference boards - pcb090 and pcb091. The SoC chip ID is used to
determine the board type.

Ocelot: This add single-binary support for the two MSCC ocelot-based
reference boards - pcb120 and pcb123. The PHY ids on specific ports
are used to determine the board type.

Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>