leon,can: introduce common CAN baud-rate calculation function

Reimplemented the baud-rate algorithm from scratch to cope with
GRCAN, GRCANFD and OC_CAN devices.

Update #4323.

bsps/include/grlib/grcan.h

@@ -1,6 +1,7 @@
 /**
  * @file
  * @ingroup can
+ * @brief Driver API for the GRLIB GRCAN and GRCANFD controllers
  */
 
 /*
@@ -25,6 +26,8 @@
  * @{
  */
 
+#include <stdint.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif