pseq: Add power control dbus server interface

Add the PowerInterface class which provides a server interface for the
"org.openbmc.control.Power" dbus service.

Update meson.build file to support.

The "org.openbmc.control.Power" interface is currently used by the
Chassis component to control power on and off as well as by a number of
other OBMC applications which use the pgood property and associated
signals to determine the power state of the system.  Some desire to
move to a "xyz.openbmc_project.control.Power" interface has been
expressed.  The following is a proposed plan to accomplish this:
1. Create a compatible "org.openbmc.control.Power" application (this
   commit).
2. Add "xyz..." interface to this application (future commit).
3. Begin transition of existing applications to new interface (future
   commits).

Signed-off-by: Jim Wright <jlwright@us.ibm.com>
Change-Id: Ia9a6bbb58b5e439623d3931426cb91cb8948da7a
diff --git a/phosphor-power-sequencer/src/meson.build b/phosphor-power-sequencer/src/meson.build
index 6b42151..f3e0d26 100644
--- a/phosphor-power-sequencer/src/meson.build
+++ b/phosphor-power-sequencer/src/meson.build
@@ -7,6 +7,7 @@
     'phosphor-power-control',
     'power_control_main.cpp',
     'power_control.cpp',
+    'power_interface.cpp',
     dependencies: [
         phosphor_logging,
         sdbusplus,