pseq: Support "GPIOs only" power sequencer device

Add support for a "GPIOs only" power sequencer device to the
phosphor-power-sequencer application.

If this device type is specified in the JSON con

pseq: Support "GPIOs only" power sequencer device

Add support for a "GPIOs only" power sequencer device to the
phosphor-power-sequencer application.

If this device type is specified in the JSON configuration file, then
the application will only use the named GPIOs to power the device on/off
and read the power good signal. No attempt will be made to communicate
with the device otherwise. No pgood fault isolation will be performed.

This device type is useful for simple systems that do not require pgood
fault isolation. It is also useful as a temporary solution when
performing early bring-up work on a new system.

Tested:
* Ran automated tests

Change-Id: Ib5ba9a9c136dd5f5e853372f881f9e227f01a6bd
Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>

show more ...