PNP: make generic pnp_add_mem_resource()

Add a pnp_add_mem_resource() that can be used by all the PNP
backends.  This consolidates a little more pnp_resource_table
knowledge into one place.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>