drm/i915: fix sparse warnings: move 'extern' decls to header file

Move 'extern'-decls from "intel_dvo.c" to "dvo.h", as "dvo.h" is
included by and only by files where the symbols are either defined or
used.

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/gpu/drm/i915/dvo.h

@@ -148,4 +148,10 @@ struct intel_dvo_dev_ops {
 	void (*dump_regs)(struct intel_dvo_device *dvo);
 };
 
+extern struct intel_dvo_dev_ops sil164_ops;
+extern struct intel_dvo_dev_ops ch7xxx_ops;
+extern struct intel_dvo_dev_ops ivch_ops;
+extern struct intel_dvo_dev_ops tfp410_ops;
+extern struct intel_dvo_dev_ops ch7017_ops;
+
 #endif /* _INTEL_DVO_H */