ui/surface: allocate shared memory on !win32

ui/surface: allocate shared memory on !win32

Use qemu_memfd_alloc() to allocate the display surface memory, which
will fallback on tmpfile/mmap() on systems without memfd, and allow to
share the display with other processes.

This is similar to how display memory is allocated on win32 since commit
09b4c198 ("console/win32: allocate shareable display surface").

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-ID: <20241008125028.1177932-13-marcandre.lureau@redhat.com>