[OpenPower-Firmware] Dropping Power8 in op-build

[Joel Stanley]

Hello openpower firmware list,

I maintain the buildroot overlay used in op-build, which normally
follows upstream releases. Buildroot 2019.05 was the last release with
GCC 6 support and hostboot for Power8 does not build with newer
versions of GCC, so in order to keep Power8 in the tree we've not
moved forward for some time now.

There is currently no one working on fixing hostboot. Without someone
stepping forward, we will have to drop support for building Power8
hostboot in op-build master.

Meaningfully, this would mean removing the Power8 platforms. The
non-hostboot components (skiboot, the kernel, the rootfs) are
processor family agnostic, so the opal_defconfig could be used to
generate firmware for Power8 machines should there be a desire.

The Hostboot codebase for Power8 is not changing. If you would like to
volunteer getting it building, once it builds the ongoing maintenance
would be minimal.

If no one steps up, I'll bump buildroot at the end of January.

Cheers,

Joel