eal/pci: introduce a PCI driver flag

eal/pci: introduce a PCI driver flag

Some ethdev devices like nicvf thunderx PMD need special treatment for
Secondary queue set(SQS) PCIe VF devices, where, it expects to not unmap
or free the memory without registering the ethdev subsystem.

Introducing a new RTE_PCI_DRV_KEEP_MAPPED_RES
PCI driver flag to request PCI subsystem to not unmap the mapped PCI
resources(PCI BAR address) if unsupported device detected.

Suggested-by: Ferruh Yigit <ferruh.yigit@intel.com>
Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>