target/mips: Deprecate nanoMIPS ISA

target/mips: Deprecate nanoMIPS ISA

The nanoMIPS ISA has been announced in 2018 for various projects:

GCC:   https://gcc.gnu.org/legacy-ml/gcc/2018-05/msg00012.html
Linux: https://lwn.net/Articles/753605/
QEMU:  https://www.mail-archive.com/qemu-devel@nongnu.org/msg530721.html

Unfortunately the links referenced doesn't work anymore (www.mips.com).

From this Wayback machine link [1] we can get to a working place to
download a toolchain (a more recent release than the one referenced
in the announcement mails):
http://codescape.mips.com/components/toolchain/nanomips/2018.04-02/downloads.html

The toolchain page mention LLVM but simply links http://llvm.org/
where there is no reference on nanoMIPS.

The only reference in the GCC mailing list, is the nanoMIPS
announcement: https://gcc.gnu.org/pipermail/gcc/2018-May.txt

The developer who authored the announcements have been emailed [2]
to ask for more information but all their emails are now bouncing:

- Your message to Stefan.Markovic@mips.com couldn't be delivered.

- Your message to smarkovic@wavecomp.com couldn't be delivered.

- Couldn't deliver the message to the following recipients:
    Robert.Suchanek@mips.com, matthew.fortune@mips.com,
    marcin.nowakowski@mips.com

Our deprecation policy do not allow feature removal before 2 release,
therefore declare the nanoMIPS ISA code deprecated as of QEMU 5.2.
This gives time to developers to update the QEMU community, or
interested parties to step in to maintain this code.

[1] https://web.archive.org/web/20180904044530/https://www.mips.com/develop/tools/compilers/
[2] https://www.mail-archive.com/qemu-devel@nongnu.org/msg756392.html

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20201102202710.2224691-1-f4bug@amsat.org>