pinctrl: ocelot: add clock monitor option for LAN966x

The SoC supports a debug clock output of its internal clocks. Depending
on the clk_sel input (GPIO_31) clk_mon (GPIO_30) will output either
cpu_clk/64 or sys_clk/64. This is very useful for debugging and is
missing in the pinmux table. Add it.

Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20220326192848.2944519-2-michael@walle.cc


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>