Use generic spin () instead of amd64_spin ()

kernel/amd64/apic.c

@@ -7,6 +7,7 @@
 #include <sys/debug.h>
 #include <sys/mm.h>
 #include <sys/time.h>
+#include <sys/spin.h>
 #include <uacpi/acpi.h>
 #include <uacpi/status.h>
 #include <uacpi/tables.h>
@@ -45,10 +46,6 @@ static size_t intr_src_override_entries = 0;
 /// Local APIC MMIO base address. It comes from MSR_APIC_BASE
 static uintptr_t lapic_mmio_base = 0;
 
-/** @cond DOXYGEN_IGNORE */
-extern void amd64_spin (void);
-/** @endcond */
-
 /// Read IOAPIC
 static uint32_t amd64_ioapic_read (uintptr_t vaddr, uint32_t reg) {
   *(volatile uint32_t*)vaddr = reg;
@@ -177,7 +174,7 @@ void amd64_ioapic_init (void) {
   uacpi_status status = uacpi_table_find_by_signature (ACPI_MADT_SIGNATURE, &apic_table);
   if (status != UACPI_STATUS_OK) {
     DEBUG ("Could not find MADT table!\n");
-    amd64_spin ();
+    spin ();
   }
 
   struct acpi_madt* apic = (struct acpi_madt*)apic_table.virt_addr;