hwmon: (pmbus/adm1266) add debugfs for states

Add a debugfs entry which prints the current state
of the adm1266 sequencer.

Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Link: https://lore.kernel.org/r/20200812142055.9213-5-alexandru.tachici@analog.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>