docs/about/deprecated.rst: document isapc deprecation for modern x86 CPU models
Add a new paragraph in the "Backwards compatibility" section documenting that
using modern x86 CPU models with the isapc machine is deprecated, and will be
rejected in a future release.
Signed-off-by: Mark Cave-Ayland <mark.caveayland@nutanix.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/20251023142926.964718-3-mark.caveayland@nutanix.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>