enable set systick priority for bumblebee

arch/risc-v/spike/gcc/riscv_port_c.c

@@ -1,3 +1,9 @@
-void riscv_cpu_init() {
+#include "tos.h"
+
+__PORT__ void port_cpu_init() {
+    // DO NOTHING
+}
+
+__PORT__ void port_systick_priority_set(uint32_t priority) {
     // DO NOTHING
 }