vdpa/mlx5: replace pthread functions unavailable in musl

vdpa/mlx5: replace pthread functions unavailable in musl

1/ The function pthread_yield() does not exist in musl libc,
and can be replaced with sched_yield() after including sched.h.

2/ The function pthread_attr_setaffinity_np() does not exist in musl libc,
and can be replaced with pthread_setaffinity_np() after pthread_create().

Fixes: b7fa0bf4d5c6 ("vdpa/mlx5: fix polling threads scheduling")
Fixes: 5cf3fd3af4df ("vdpa/mlx5: add CPU core parameter to bind polling thread")
Cc: stable@dpdk.org
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Matan Azrad <matan@nvidia.com>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: David Marchand <david.marchand@redhat.com>