Add pmbus driver support for Maxim MAX15301 InTune Automatically
Compensated Digital PoL Controller with Driver and PMBus Telemetry

Even though the specification does not specifically mention it,
extensive empirical testing has revealed that auto-detection of
limit-registers will fail in a random fashion unless the delay
parameter is set to above about 80us. The default delay is set
to 100us to include some safety margin.

This patch is tested on a Flex BMR461 converter module.
Signed-off-by: Erik Rosen <erik.rosen@metormote.com>
Link: https://lore.kernel.org/r/20210419101251.24840-1-erik.rosen@metormote.com
[groeck: Added rationale for delay to driver header]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>