[pcbios] Do not switch to real mode to sleep the CPU

Now that we can handle interrupts while in protected mode, there is no
need to switch to real mode just to halt the CPU.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/interface/pcbios/bios_nap.c

  *
  */
 static void bios_cpu_nap ( void ) {
-	__asm__ __volatile__ ( REAL_CODE ( "sti\n\t"
-					   "hlt\n\t"
-					   "cli\n\t" ) : : );
+	__asm__ __volatile__ ( "sti\n\t"
+			       "hlt\n\t"
+			       "cli\n\t" );
 }
 
 PROVIDE_NAP ( pcbios, cpu_nap, bios_cpu_nap );