vhost: switch vhost get_indirect() to iov_iter, kill memcpy_fromiovec()

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: kvm@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc drivers/vhost/vhost.c
Simple merge

diff --cc include/linux/uio.h
Simple merge

diff --cc lib/iovec.c
Simple merge