Check for null pointers when printing.

Don't crash when given an fi_info with null pointers in struct fields. Came across this when printing the stack-allocated hints fi_info.

Signed-off-by: pmmccorm <patrick.m.mccormick@intel.com>
Clean up rdma/fi_prov.h include.

Add missing fi_register_provider def to fabric.h, use in fi_prov instead of defining there.

Signed-off-by: pmmccorm <patrick.m.mccormick@intel.com>