powerpc: drop MPC837x_MDS platform support

powerpc: drop MPC837x_MDS platform support

This next evolutionary step in the e300 family of Modular Development
System (MDS) still has, at its core component, a full length card with a
PCI edge.  No case.  Serial and network connectors were on card, so it
could optionally be fitted with plastic stand-offs and run stand-alone
off a power brick.

This is very similar to the MPC834x_MDS and MPC836x_MDS removed in the
prior commits, but with this board variant as yet another evolutionary
step.  SATA and PCI-e were now available.  But overall the form factor
and design goals were unchanged.

Like all the MDS systems, it was meant as a vehicle to get the CPU out
early to hardware OEMs so software and board development could take place
in parallel.

These were made in limited numbers and availability preference was given
to partners who were planning to make their own boards.

Given that the whole reason for existence was to assist in enabling new
board designs [not happening for 10+ years], and that they weren't
generally available, and that the hardware wasn't really hobbyist friendly
even for retro computing, it makes sense to retire the support for this
particular platform.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230220115913.25811-4-paul.gortmaker@windriver.com