AP_HAL: move set_retries() up to Device class

we really need set_retries() high during init for nearly all i2c
devices, and as many are written against the generic device class
moving it to the Device class makes this a lot easier. It is a NOP on
SPI.

libraries/AP_HAL/Device.h

@@ -235,6 +235,9 @@ public:
     uint32_t get_bus_id_devtype(uint8_t devtype) {
         return change_bus_id(get_bus_id(), devtype);
     }
+
+    /* set number of retries on transfers */
+    virtual void set_retries(uint8_t retries) {};
     
 protected:
     uint8_t _read_flag = 0;

libraries/AP_HAL/I2CDevice.h

@@ -36,9 +36,6 @@ public:
      */
     virtual void set_address(uint8_t address) = 0;
 
-    /* set number of retries on transfers */
-    virtual void set_retries(uint8_t retries) = 0;
-
     /* Device implementation */
 
     /* See Device::set_speed() */