linux: Fix futex() command bitmask

The "op" argument passed to futex() also include flags so we need to
mask the command bits.

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
linux: Wire up uname system call

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
tools/uush: add cd builtin and ls, mkdir binaries

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>