eal: enable port hotplug as default for linux and bsd

eal: enable port hotplug as default for linux and bsd

This patch removes CONFIG_RTE_LIBRTE_EAL_HOTPLUG option, and enables it
as default in both Linux and BSD.
Also, to support port hotplug, rte_eal_pci_scan() and below missing
symbols should be exported to ethdev library.
 - rte_eal_parse_devargs_str()
 - rte_eal_pci_close_one()
 - rte_eal_pci_probe_one()
 - rte_eal_pci_scan()
 - rte_eal_vdev_init()
 - rte_eal_vdev_uninit()

Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>