doc: announce API changes for device objects
doc: announce API changes for device objects

Following discussions with Jan, here is a deprecation notice to prepare for
hotplug and rte_device changes to come in 16.07.

Signed-off-by: David Marchand <f28529695cfa9e3e1eb84e7072aa626af4abb18e@6wind.com>
Acked-by: Jan Viktorin <077cce75738556d99b8362c6a64d5bba1ba87459@rehivetech.com>
Acked-by: Olivier Matz <dfcc1510895413197abb4336e39bb0a3906cba71@6wind.com>
Acked-by: Thomas Monjalon <ee2fa8b2681c737f775687e475dcbf2028a412f1@6wind.com>

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