bsp,abstract-machine: add dummy functions to pass linking

bsp/abstract-machine/src/context.c

@@ -0,0 +1,19 @@
+#include <klib.h>
+#include <rtthread.h>
+
+void rt_hw_context_switch_to(rt_ubase_t to) {
+  assert(0);
+}
+
+void rt_hw_context_switch(rt_ubase_t from, rt_ubase_t to) {
+  assert(0);
+}
+
+void rt_hw_context_switch_interrupt(void *context, rt_ubase_t from, rt_ubase_t to, struct rt_thread *to_thread) {
+  assert(0);
+}
+
+rt_uint8_t *rt_hw_stack_init(void *tentry, void *parameter, rt_uint8_t *stack_addr, void *texit) {
+  assert(0);
+  return NULL;
+}

bsp/abstract-machine/src/init.c

@@ -1,3 +1,9 @@
+#include <klib.h>
+
+void rt_hw_board_init() {
+  assert(0);
+}
+
 int main() {
   extern int entry(void);
   entry();

bsp/abstract-machine/src/interrupt.c

@@ -0,0 +1,10 @@
+#include <am.h>
+#include <klib.h>
+
+void rt_hw_interrupt_enable() {
+  assert(0);
+}
+
+void rt_hw_interrupt_disable() {
+  assert(0);
+}