PNP: Compile all pnp built-in stuff in one module namespace

This is cleanup mostly, nothing urgent.
I came up with it when looking at dynamic debug which can
enable pr_debug messages at runtime or boot param
for a specific module.

Advantages:
  - Any pnp code can make use of the moduleparam.h interface, the modules
    will show up as pnp.param.
  - Passing pnp.ddebug as kernel boot param will enable all pnp debug messages
    with my previous patch and CONFIG_DYNAMIC_DEBUG enabled.

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