docs/system: Deprecate raspi2/raspi3 machine aliases

Since commit aa35ec2 ("hw/arm/raspi: Use more specific
machine names") the raspi2/raspi3 machines have been renamed
as raspi2b/raspi3b.

Note, rather than the raspi3b, the raspi3ap introduced in
commit 5be9425 ("hw/arm/raspi: Add the Raspberry Pi 3
model A+") is a closer match to what QEMU models, but only
provides 512 MB of RAM.

As more Raspberry Pi 2/3 models are emulated, in order
to avoid confusion, deprecate the raspi2/raspi3 machine
aliases.

ACKed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20201120173953.2539469-2-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

docs/system/deprecated.rst

@@ -346,6 +346,13 @@ This machine has been renamed ``fuloong2e``.
 These machine types are very old and likely can not be used for live migration
 from old QEMU versions anymore. A newer machine type should be used instead.
 
+Raspberry Pi ``raspi2`` and ``raspi3`` machines (since 5.2)
+'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
+
+The Raspberry Pi machines come in various models (A, A+, B, B+). To be able
+to distinguish which model QEMU is implementing, the ``raspi2`` and ``raspi3``
+machines have been renamed ``raspi2b`` and ``raspi3b``.
+
 Device options
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