powerpc: drop HPC II (MPC7448) evaluation platform support.

This was an interesting platform - it was the 1st instance of a
respin of earlier 130nm 74xx CPUs on 90nm and systems using MPC7448
were positioned as a rack server platform solution.

Given that, the evaluation platform (at least the one I had) was shipped
in a horizontal 1/2 height Antec desktop case with retro styling and
colours, despite the fact the docs explicitly stated that the HPC II is
not a desktop machine (noting it had no gfx or legacy PC I/O support).

Historic trivia aside, this was the 1st introduction of the e600
procfam as an evolution from the earlier G4.

However even with the claim to being "1st e600" it seems the 2005+
era was turning its attention to multicore support and from my memory
this poor guy was quickly overshadowed by the dual core MPC8641D.

All that aside, we are once again looking at 15+ year old evaluation
platforms that were not widely distributed, so 2023 removal makes sense.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230225201318.3682-2-paul.gortmaker@windriver.com