ARM: OMAP2+: gpmc: minimal driver support

Create a minimal driver out of gpmc code.  Responsibilities handled by
earlier gpmc initialization is now achieved in probe.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Reviewed-by: Jon Hunter <jon-hunter@ti.com>
[paul@pwsan.com: fixed some checkpatch messages]
Signed-off-by: Paul Walmsley <paul@pwsan.com>