sys/phydat: Add capacitance unit (F)

sys/include/phydat.h

@@ -96,6 +96,7 @@ enum {
     UNIT_GS,        /**< gauss */
     UNIT_DBM,       /**< decibel-milliwatts */
     UNIT_COULOMB,   /**< coulomb */
+    UNIT_F,         /**< Farad */
     /* pressure */
     UNIT_BAR,       /**< Beer? */
     UNIT_PA,        /**< Pascal */

sys/phydat/phydat_str.c

@@ -103,6 +103,7 @@ const char *phydat_unit_to_str(uint8_t unit)
         case UNIT_CTS:      return "cts";
         case UNIT_COULOMB:  return "C";
         case UNIT_GPM3:     return "g/m^3";
+        case UNIT_F:        return "F";
         default:            return "";
     }
 }