hwmon: (pmbus) Do not set regulators_node for single-channel chips

hwmon: (pmbus) Do not set regulators_node for single-channel chips

Single-channel regulators do not need and should not have a "regulators"
node. We can not entirely remove it due to existing bindings. To solve the
problem for new drivers, provide additional macros PMBUS_REGULATOR_ONE_NODE
and PMBUS_REGULATOR_STEP_ONE_NODE and convert existing drivers to use those
macros. The exception is the ir38064 driver because its devicetree files
and its description do not require or use the nested regulators node.

Modify PMBUS_REGULATOR_STEP_ONE and PMBUS_REGULATOR_ONE to set the
regulators_node pointer to NULL.

Cc: Cedricjustine.Encarnacion@analog.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20250322142602.560042-1-linux@roeck-us.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>