doc: Add more functions to fpi-dev section

And rename section to match that of fpi-dev-img

doc/libfprint-sections.txt

@@ -195,6 +195,10 @@ FP_DEV
 FP_IMG_DEV
 fp_dev_set_instance_data
 FP_INSTANCE_DATA
+
+fpi_dev_get_usb_dev
+fpi_dev_get_verify_data
+fpi_dev_set_nr_enroll_stages
 </SECTION>
 
 <SECTION>

libfprint/fpi-dev.c

@@ -22,7 +22,7 @@
 
 /**
  * SECTION:fpi-dev
- * @title: Device structures
+ * @title: Device operations
  *
  * Those macros and functions will help get access to and from struct #fp_dev,
  * and struct #fp_img_dev types, as well as get and set the instance struct