OMAP: DSS2: omap_dss_probe() conditional compilation cleanup

Move a number of #ifdefs from code into dss.h and elsewhere, and
conditionally define no-op static inline functions, cleaning up the
code. This style is according to Documentation/SubmittingPatches.

Signed-off-by: Jani Nikula <ext-jani.1.nikula@nokia.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>