Replace Qemu -> QEMU.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20211118143401.4101497-1-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>