AP_HAL: move get_device() method from AP_HAL_Linux

This way it's possible to use the method in platform-independent code
without a need to up cast.

libraries/AP_HAL/I2CDevice.h

@@ -17,6 +17,7 @@
 #pragma once
 
 #include <inttypes.h>
+#include <vector>
 
 #include "AP_HAL_Namespace.h"
 #include "Device.h"
@@ -75,6 +76,19 @@ public:
                                                  uint32_t bus_clock=400000,
                                                  bool use_smbus = false,
                                                  uint32_t timeout_ms=4) = 0;
+    /*
+     * Get device by looking up the I2C bus on the buses from @devpaths.
+     *
+     * Each string in @devpaths are possible locations for the bus. How the
+     * strings are implemented are HAL-specific. On Linux this is the info
+     * returned by 'udevadm info -q path /dev/i2c-X'. The first I2C bus
+     * matching a prefix in @devpaths is used to create a I2CDevice object.
+     */
+    virtual OwnPtr<I2CDevice> get_device(std::vector<const char *> devpaths,
+                                         uint8_t address) {
+        // Not implemented
+        return nullptr;
+    }
 };
 
 }

libraries/AP_HAL_Linux/I2CDevice.h

@@ -94,15 +94,8 @@ public:
 
     I2CDeviceManager();
 
-    /*
-     * Get device by looking up the I2C bus on the buses from @devpaths.
-     *
-     * Each string in @devpaths are possible locations for the bus as
-     * returned by 'udevadm info -q path /dev/i2c-X'. The first I2C bus
-     * matching a prefix in @devpaths is returned.
-     */
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> get_device(
-            std::vector<const char *> devpaths, uint8_t address);
+            std::vector<const char *> devpaths, uint8_t address) override;
 
     /* AP_HAL::I2CDeviceManager implementation */
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> get_device(uint8_t bus, uint8_t address,