PNP: add pnp_alloc_card()

Add pnp_alloc_card() to allocate a struct pnp_card and fill in the
protocol, instance number, and initial PNP ID.  Now it is always
valid to use dev_printk() on any pnp_card pointer.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Acked-By: Rene Herman <rene.herman@gmail.com>
Signed-off-by: Len Brown <len.brown@intel.com>