memory: Simplify memory_region_init_rom_nomigrate() to ease review

memory_region_init_rom_nomigrate() has the same content than
memory_region_init_ram_shared_nomigrate(), with setting the
readonly mode. The code is easier to review as creating a
readonly ram/shared/nomigrate region.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
1 file changed