doc: announce deprecation of coherent I/O memory barriers
doc: announce deprecation of coherent I/O memory barriers

rte_cio_*mb APIs will be deprecated in 20.11 release.

Signed-off-by: Honnappa Nagarahalli <01ccf438b971cc1d8919c8a7f18443cae9429d8b@arm.com>
Acked-by: Jerin Jacob <352c4d4f9291b869992ddb67daa45ddc149fed30@marvell.com>
Reviewed-by: David Christensen <9a876b0e626a7e524926f129e2e0ea9c4c104ff4@linux.vnet.ibm.com>
Acked-by: Ajit Khaparde <01965fbd61169dc18f3fb5e13de7f67d298f8924@broadcom.com>
Acked-by: Konstantin Ananyev <cbd5212b59ab42a210d72992d23a3aa17cfd3eaf@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk