ethdev: fix build without hotplug

ethdev: fix build without hotplug

After setting CONFIG_RTE_LIBRTE_EAL_HOTPLUG=n, GCC stop compiling:
rte_ethdev.c:430:1: error: ‘rte_eth_dev_get_device_type’ defined but not used
rte_ethdev.c:438:1: error: ‘rte_eth_dev_save’ defined but not used
rte_ethdev.c:450:1: error: ‘rte_eth_dev_get_changed_port’ defined but not used
rte_ethdev.c:464:1: error: ‘rte_eth_dev_get_addr_by_port’ defined but not used
rte_ethdev.c:481:1: error: ‘rte_eth_dev_get_name_by_port’ defined but not used
rte_ethdev.c:503:1: error: ‘rte_eth_dev_is_detachable’ defined but not used

The hotplug option allows to build in environment (BSD) not yet
supported by this new feature.
It should be removed when BSD will be supported.
Waiting this day, let's fix build with hotplug disabled.

Reported-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>