Input: rotary-encoder - add support for half-period encoders

Add support for encoders that have two detents per input signal period.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Acked-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/include/linux/rotary_encoder.h b/include/linux/rotary_encoder.h
index 215278b..3f594dc 100644
--- a/include/linux/rotary_encoder.h
+++ b/include/linux/rotary_encoder.h
@@ -10,6 +10,7 @@
 	unsigned int inverted_b;
 	bool relative_axis;
 	bool rollover;
+	bool half_period;
 };
 
 #endif /* __ROTARY_ENCODER_H__ */