pseq: Add open/close for devices

Add open and close methods for PowerSequencerDevice classes. Move any
logic that acquires system resources from the constructor to the open()
method. Release the sys

pseq: Add open/close for devices

Add open and close methods for PowerSequencerDevice classes. Move any
logic that acquires system resources from the constructor to the open()
method. Release the system resources in the close() method.

These methods are needed for several reasons:
- The JSON configuration file will define the maximum number of chassis
for a system type. If some chassis are missing, the associated power
sequencer and named GPIOs are likely also missing. The constructor
should not try to acquire system resources related to missing
hardware since it will likely result in errors.
- A chassis may be removed or lose input power. If that chassis later
becomes available again, the C++ objects representing the underlying
hardware resources may not be reusable in their current form. For
example, libgpiod may have acquired a file handle that is no longer
valid. So when a chassis becomes unavailable, the device should be
closed and any associated resources should be released. If the chassis
becomes available again, the device should be re-opened and the
resources should be re-acquired.

Tested:
* Ran automated tests
* Verified open and close methods in simulation
* Verified chassis power on and power off on hardware (regression test)

Change-Id: Ia2726d74252b4fa254b12e105daaeb961a047ee6
Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>

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pseq: Move common code to BasicDevice class

Create a new sub-class of PowerSequencerDevice called BasicDevice that
implements basic functionality.

BasicDevice implements the following:
- Data membe

pseq: Move common code to BasicDevice class

Create a new sub-class of PowerSequencerDevice called BasicDevice that
implements basic functionality.

BasicDevice implements the following:
- Data members and methods for the power sequencer properties from the
JSON configuration file.
- Methods that utilize the named GPIOs, such as powerOn() and
getPowerGood().

This functionality was previous duplicated in both StandardDevice and
GPIOsOnlyDevice. Change both of those classes to inherit from
BasicDevice.

Tested:
* Ran automated tests

Change-Id: Id80e34dca0d2412ae10abe9962eca632d1909962
Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>

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