This patch updates MIPS-based machines to allow starting them without ROM.
In this case CPU starts to execute instructions from the empty memory,
but QEMU allows introspecting the machine configuration.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <159531210571.24117.231100997794891819.stgit@pasha-ThinkPad-X280>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>