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 <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Reviewed-by: Alex Bennée <[email protected]>
Tested-by: Alex Bennée <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>
Message-id: 20200228153619[email protected]
Message-id: 20200226113034[email protected]
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>