hwmon: (ucd9000) Add gpio and debugfs interfaces

The ucd9000 series chips have gpio pins. Add a gpio chip interface to the ucd device so that users can query and set the state of the gpio pins.

Add a debugfs interface using the existing pmbus debugfs directory to provide MFR_STATUS and the status of the gpi faults to users.

Changes since v6:
- don't return null terminator for mfr_status

Changes since v5:
- enclose gpio code in #ifdef GPIOLIB
- don't initialize buffers for mfr_status; set last char to 0 instead
- cap the size argument to bin2hex

Changes since v4:
- max-sized buffers for smbus transfers
- used bin2hex instead of my own code

Changes since v3:
- remove setting of gpio_chip->owner
- format the mfr_status data
- switch to #ifdef rather than #if IS_ENABLED for debugfs

Changes since v2:
- split the gpio registration into it's own function

Changes since v1:
- dropped dev_err messages
- made gpio chip registration conditional on having gpio pins
- made mfr_status debugfs attribute more simple

Christopher Bostic (2):
hwmon: (ucd9000) Add gpio chip interface
hwmon: (ucd9000) Add debugfs attributes to provide mfr_status

 drivers/hwmon/pmbus/ucd9000.c | 350 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 349 insertions(+), 1 deletion(-)

1.8.3.1