gpio-keys-polled improvements v2

[Enrico Weigelt, metux IT consult]

Hello folks,

here's v2 of my gpio-keys-polled queue.

changes v2:

* removed the change in mod_devicetable.h
  (MODULE_DEVICE_TABLE_OF macro)
* reworked the patch for building w/o oftree, so it works
  w/o the MODULE_DEVICE_TABLE_OF macro

have fun,

--mtx