hw/arm: Deprecate various old Arm machine types

hw/arm: Deprecate various old Arm machine types

QEMU includes some models of old Arm machine types which are
a bit problematic for us because:
 * they're written in a very old way that uses numerous APIs that we
   would like to get away from (eg they don't use qdev, they use
   qemu_system_reset_request(), they use vmstate_register(), etc)
 * they've been that way for a decade plus and nobody particularly has
   stepped up to try to modernise the code (beyond some occasional
   work here and there)
 * we often don't have test cases for them, which means that if we
   do try to do the necessary refactoring work on them we have no
   idea if they even still work at all afterwards

All these machine types are also of hardware that has largely passed
away into history and where I would not be surprised to find that
e.g. the Linux kernel support was never tested on real hardware
any more.

After some consultation with the Linux kernel developers, we
are going to deprecate:

All PXA2xx machines:

akita                Sharp SL-C1000 (Akita) PDA (PXA270)
borzoi               Sharp SL-C3100 (Borzoi) PDA (PXA270)
connex               Gumstix Connex (PXA255)
mainstone            Mainstone II (PXA27x)
spitz                Sharp SL-C3000 (Spitz) PDA (PXA270)
terrier              Sharp SL-C3200 (Terrier) PDA (PXA270)
tosa                 Sharp SL-6000 (Tosa) PDA (PXA255)
verdex               Gumstix Verdex Pro XL6P COMs (PXA270)
z2                   Zipit Z2 (PXA27x)

All OMAP2 machines:

n800                 Nokia N800 tablet aka. RX-34 (OMAP2420)
n810                 Nokia N810 tablet aka. RX-44 (OMAP2420)

One of the OMAP1 machines:

cheetah              Palm Tungsten|E aka. Cheetah PDA (OMAP310)

Rationale:
 * for QEMU dropping individual machines is much less beneficial
   than if we can drop support for an entire SoC
 * the OMAP2 QEMU code in particular is large, old and unmaintained,
   and none of the OMAP2 kernel maintainers said they were using
   QEMU in any of their testing/development
 * although there is a setup that is booting test kernels on some
   of the PXA2xx machines, nobody seemed to be using them as part
   of their active kernel development and my impression from the
   email thread is that PXA is the closest of all these SoC families
   to being dropped from the kernel soon
 * nobody said they were using cheetah, so it's entirely
   untested and quite probably broken
 * on the other hand the OMAP1 sx1 model does seem to be being
   used as part of kernel development, and there was interest
   in keeping collie around

In particular, the mainstone, tosa and z2 machine types have
already been dropped from Linux.

Mark all these machine types as deprecated.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240308171621.3749894-1-peter.maydell@linaro.org