powerpc: drop HPC-NET/MPC8641D evaluation platform support

powerpc: drop HPC-NET/MPC8641D evaluation platform support

There is no denying that this was an interesting platform in its day.
Access to a SMP powerpc platform became a bit more obtainable for folks
in the BSP industry in the 2007 era, thanks to this platform.

Add to that the move to the black Antec case vs. the generic white 2005
era case of the MPC8548CDS or the retro 1950s 1/2 height horizontal case
of the HPC II, and it was pretty interesting to people like myself then.

However, like all the other evaluation platforms, the overall system
was complex out of necessity, as it tried to showcase all possible
features and use-cases.  That included an AMP option, where you could run
two bootloaders and two kernels over two serial consoles.  Peripheral
sharing got a bit more tricky when you got to the hard disk and similar.

In any case we still have the same circumstance.  A relatively rare and
expensive evaluation platform that is now 15+ years old and not out there
in large numbers in the general public.  Removal in 2023 just makes sense.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230225201318.3682-3-paul.gortmaker@windriver.com