Skeleton power control machine configuration

[Xo Wang]

Hi folks,

I was adding power sequencing and buttons for our P9 machine and I
noticed that Firestone, Garrison, and Witherspoon had patches to
op-pwrctl that replaced the net names on the power pins, added more
reset complexes, etc.

https://github.com/openbmc/openbmc/blob/master/meta-openbmc-machines/meta-openpower/meta-ibm/meta-witherspoon/recipes-phosphor/skeleton/skeleton/0001-Set-witherspoon-power-pin-and-pgood-nets.patch
https://github.com/openbmc/openbmc/blob/ced4c34ee252d0036b714425eecb0ed8bb528750/meta-openbmc-machines/meta-openpower/meta-ibm/meta-garrison/recipes-phosphor/skeleton/skeleton/0001-Add-power-control-support-for-the-Garrison-system.patch

I didn't want to do the same for our machine. I propose moving machine
specific options to the Python configuration so we can eliminate the
skeleton patches.

I mailed my prototype to the Gerrit that adds a dbus call to
system_manager, C bindings, and power control logic to handle the
abstraction. Please take a look.

https://gerrit.openbmc-project.xyz/#/c/605/
https://gerrit.openbmc-project.xyz/#/c/606/
https://gerrit.openbmc-project.xyz/#/c/607/
https://gerrit.openbmc-project.xyz/#/c/608/

I'm planning to also extend the GPIO/net name abstraction to reset and
power buttons, since they're also using net names directly in their
sources.

cheers
xo