AP_HAL: add init() method without argument

The argument in init() is not used by any implementation. Add a second
method without it so the HAL implementation can used it instead. Later
the unused method will be removed.

libraries/AP_HAL/AnalogIn.h

@@ -41,7 +41,8 @@ public:
 
 class AP_HAL::AnalogIn {
 public:
-    virtual void init(void* implspecific) = 0;
+    virtual void init(void* implspecific) { }
+    virtual void init() { }
     virtual AP_HAL::AnalogSource* channel(int16_t n) = 0;
 
     // board 5V rail voltage in volts

libraries/AP_HAL/RCInput.h

@@ -15,7 +15,8 @@ public:
      * known to the programmer. (Its too difficult to describe this dependency
      * in the C++ type system.)
      */
-    virtual void init(void* implspecific) = 0;
+    virtual void init(void* implspecific) { }
+    virtual void init() { }
     virtual void deinit() {};
 
     /**

libraries/AP_HAL/RCOutput.h

@@ -32,7 +32,8 @@
 
 class AP_HAL::RCOutput {
 public:
-    virtual void init(void* implspecific) = 0;
+    virtual void init(void* implspecific) { }
+    virtual void init() { }
 
     /* Output freq (1/period) control */
     virtual void     set_freq(uint32_t chmask, uint16_t freq_hz) = 0;

libraries/AP_HAL/SPIDriver.h

@@ -7,7 +7,8 @@
 
 class AP_HAL::SPIDeviceManager {
 public:
-    virtual void init(void *) = 0;
+    virtual void init(void *) { }
+    virtual void init() { }
     virtual AP_HAL::SPIDeviceDriver* device(enum AP_HAL::SPIDevice, uint8_t index = 0) = 0;
 };
 

libraries/AP_HAL/Scheduler.h

@@ -13,7 +13,8 @@
 class AP_HAL::Scheduler {
 public:
     Scheduler() {}
-    virtual void     init(void* implspecific) = 0;
+    virtual void     init(void* implspecific) { }
+    virtual void     init() { }
     virtual void     delay(uint16_t ms) = 0;
 
     /*

libraries/AP_HAL/Storage.h

@@ -7,7 +7,8 @@
 
 class AP_HAL::Storage {
 public:
-    virtual void init(void *) = 0;
+    virtual void init(void *) { }
+    virtual void init() { }
     virtual void read_block(void *dst, uint16_t src, size_t n) = 0;
     virtual void write_block(uint16_t dst, const void* src, size_t n) = 0;
 };