Wrap PNP probe code in #ifdef CONFIG_PNP.

Without this change, we'll have unresolved references to pnp_get_resource()
function when CONFIG_PNP=n.  (This is a new interface that's not in mainline
yet.)
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>