Add support I2C ARMmbed#3 (#ifdef I2C2) for target EFM32G11

Author: petroborys

targets/TARGET_Silicon_Labs/TARGET_EFM32/i2c_api.c

@@ -63,6 +63,11 @@ static uint8_t i2c_get_index(i2c_t *obj)
         case I2C_1:
             index = 1;
             break;
+#endif
+#ifdef I2C2
+        case I2C_2:
+            index = 2;
+            break;
 #endif
         default:
             printf("I2C module not available.. Out of bound access.");
@@ -84,6 +89,11 @@ static CMU_Clock_TypeDef i2c_get_clock(i2c_t *obj)
         case I2C_1:
             clock = cmuClock_I2C1;
             break;
+#endif
+#ifdef I2C2
+        case I2C_2:
+            clock = cmuClock_I2C2;
+            break;
 #endif
         default:
             printf("I2C module not available.. Out of bound access. (clock)");
@@ -175,6 +185,11 @@ void i2c_enable_interrupt(i2c_t *obj, uint32_t address, uint8_t enable)
         case 1:
             irq_number = I2C1_IRQn;
             break;
+#endif
+#ifdef I2C2
+        case 2:
+            irq_number = I2C2_IRQn;
+            break;
 #endif
     }