[main] save some cycles on the physical hardware

kernel/main.c

@@ -160,6 +160,7 @@ int main(struct multiboot *mboot_ptr, uint32_t mboot_mag, uintptr_t esp)
 			kprintf("[%d:%d:%d]", hours, minutes, seconds);
 			restore_csr();
 			__asm__ __volatile__ ("sti");
+			__asm__ __volatile__ ("hlt");
 		}
 	} else {
 		start_shell();