hwmon: (pmbus): Add generic alarm bit for iin and pin

Add PB_STATUS_INPUT as the generic alarm bit for iin and pin. We also
need to redo the status register checking before setting up the boolean
attribute, since it won't necessarily check STATUS_WORD if the device
doesn't support it, which we need for this bit.

Signed-off-by: Edward A. James <eajames@us.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>