eal: remove duplicate function declaration

rte_eal_dev_init is declared in both eal_private.h and rte_dev.h since its
introduction.
This function has been exported in ABI, so remove it from eal_private.h

Fixes: e57f20e05177 ("eal: make vdev init path generic for both virtual and pci devices")

Signed-off-by: David Marchand <david.marchand@6wind.com>
Signed-off-by: Shreyansh Jain <shreyansh.jain@nxp.com>
Reviewed-by: Jan Viktorin <viktorin@rehivetech.com>