mraa.c: Add mraa_get_platform_version call

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

api/mraa/common.h

@@ -142,6 +142,16 @@ mraa_result_t mraa_set_log_level(int level);
  */
 char* mraa_get_platform_name();
 
+/**
+ * Return the platform's versioning info, the information given depends per
+ * platform and can be NULL. platform_offset has to be given. Do not modify
+ * this pointer
+ *
+ * @param specified platform offset; 0 for main platform, 1 for sub platform
+ * @return platform's versioning string
+ */
+const char* mraa_get_platform_version(int platform_offset);
+
 /**
  * This function attempts to set the mraa process to a given priority and the
  * scheduler to SCHED_RR. Highest * priority is typically 99 and minimum is 0.