target/mips: Deprecate Trap-and-Emul KVM support

Upstream kernel had removed both host[1] and guest[2] support.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/mips/linux.git/commit/?id=45c7e8af4a5e3f0bea4ac209eea34118dd57ac64
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/mips/linux.git/commit/?id=a1515ec7204edca770c07929df8538fcdb03ad46



Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210317011235.7425-1-jiaxun.yang@flygoat.com>
[PMD: Specify mentioned kernel is Linux]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

docs/system/deprecated.rst

@@ -186,6 +186,15 @@ Use the more generic commands ``block-export-add`` and ``block-export-del``
 instead.  As part of this deprecation, where ``nbd-server-add`` used a
 single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
 
+System accelerators
+-------------------
+
+MIPS ``Trap-and-Emul`` KVM support (since 6.0)
+''''''''''''''''''''''''''''''''''''''''''''''
+
+The MIPS ``Trap-and-Emul`` KVM host and guest support has been removed
+from Linux upstream kernel, declare it deprecated.
+
 System emulator CPUS
 --------------------