add constants for brightness in C api

crates/servicepoint_binding_c/examples/lang_c/include/servicepoint.h

@@ -8,6 +8,21 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+/**
+ * Count of possible brightness values
+ */
+#define SP_BRIGHTNESS_LEVELS 12
+
+/**
+ * see [Brightness::MAX]
+ */
+#define SP_BRIGHTNESS_MAX 11
+
+/**
+ * see [Brightness::MIN]
+ */
+#define SP_BRIGHTNESS_MIN 0
+
 /**
  * pixel count on whole screen
  */