AP_Common: AP_FWVersion: add pointers to git hash strings

Keeping the hash strings on this struct allow to handle them
the same way on common code and remove ifdefs.

libraries/AP_Common/AP_FWVersion.h

@@ -11,4 +11,7 @@ typedef struct {
     uint8_t patch;
     FIRMWARE_VERSION_TYPE fw_type;
     const char *fw_string;
+    const char *fw_hash_str;
+    const char *middleware_hash_str;
+    const char *os_hash_str;
 } AP_FWVersion;