PNP: add pnp_get_resource() interface

This adds a pnp_get_resource() that works the same way as
platform_get_resource().  This will enable us to consolidate
many pnp_resource_table references in one place, which will
make it easier to make the table dynamic.

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>