flavours/linux: Fix runqemu arguments to run without X11

runqemu's nographic option sets qemu argument `display` to `none` and
this allows to use runqemu script in headless environment (without X11)
Using nographic qemuparam doesn't affect display setting and `sdl` is
used which causes `Could not initialize SDL(x11 not available) -
exiting` error

Signed-off-by: Pavel Zhukov <pavel.zhukov@huawei.com>