Use generic spin () instead of amd64_spin ()

kernel/amd64/intr.c

@@ -9,6 +9,7 @@
 #include <sys/debug.h>
 #include <sys/irq.h>
 #include <sys/smp.h>
+#include <sys/spin.h>
 
 /* 8259 PIC defs. */
 #define PIC1      0x20
@@ -58,10 +59,6 @@ ALIGNED (16) static volatile struct idt_entry idt_entries[IDT_ENTRIES_MAX];
 /** @endcond */
 static volatile struct idt idt;
 
-/** @cond DOXYGEN_IGNORE */
-extern void amd64_spin (void);
-/** @endcond */
-
 /// Remaps and disables old 8259 PIC, since we'll be using APIC.
 static void amd64_init_pic (void) {
   /** @cond DOXYGEN_IGNORE */
@@ -169,7 +166,7 @@ static void amd64_intr_exception (struct saved_regs* regs) {
   if (regs->cs == (0x18 | 0x03)) {
     proc_kill (thiscpu->proc_current);
   } else {
-    amd64_spin ();
+    spin ();
   }
 }