qemu-doc: split qemu-doc.texi in multiple files

qemu-doc: split qemu-doc.texi in multiple files

In order to facilitate the reorganization of qemu-doc.texi content,
as well as the conversion to rST/Sphinx, split it in multiple .texi
files that are included from docs/system.

The "other devices" section is renamed to ivshmem and placed last.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200228153619.9906-6-peter.maydell@linaro.org
Message-id: 20200226113034.6741-6-pbonzini@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>