x64: add an accessor for the special sti; hlt sequence

Also add an arch independent name for it.

arch/x64/arch.hh

@@ -18,6 +18,11 @@ inline void irq_enable()
     processor::sti();
 }
 
+inline void wait_for_interrupt()
+{
+    processor::sti_hlt();
+}
+
 class irq_flag {
 public:
     // need to clear the red zone when playing with the stack. also, can't

arch/x64/processor.hh

@@ -158,6 +158,10 @@ namespace processor {
 	    asm volatile ("cli; hlt");
 	}
 
+	inline void sti_hlt() {
+	    asm volatile ("sti; hlt");
+	}
+
 	inline u8 inb (u16 port)
 	{
 		u8 r;