NFC: hci: Add stop_poll HCI operand.

stop_poll allows to stop CLF reader polling. Some other operations might be
necessary for some CLF to stop polling. For example in card mode.

Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>