Deprecate lm32 port

Deprecate lm32 port

Deprecate our lm32 target support. Michael Walle (former lm32 maintainer)
suggested that we do this in 2019:
 https://www.mail-archive.com/qemu-devel@nongnu.org/msg605024.html
because the only public user of the architecture is the many-years-dead
milkymist project. (The Linux port to lm32 was never merged upstream.)

In commit 4b4d96c776f552e (March 2020) we marked it as 'orphan' in
the MAINTAINERS file, but didn't officially deprecate it. Mark it
deprecated now, with the intention of removing it from QEMU in
mid-2021 before the 6.1 release.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Acked-by: Michael Walle <michael@walle.cc>
Message-id: 20200827113259.25064-1-peter.maydell@linaro.org