tools/vm/page-types: remove dependency on opt_file for idle page tracking

Idle page tracking can also be used for process address space, not only
file mappings.

Without this change, using with '-i' option for process address space
encounters below errors reported.

$ sudo ./page-types -p $(pidof bash) -i
mark page idle: Bad file descriptor
mark page idle: Bad file descriptor
mark page idle: Bad file descriptor
mark page idle: Bad file descriptor
...

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Changbin Du <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

tools/vm/page-types.c

···
 	if (opt_list && opt_list_mapcnt)
 		kpagecount_fd = checked_open(PROC_KPAGECOUNT, O_RDONLY);
 
-	if (opt_mark_idle && opt_file)
+	if (opt_mark_idle)
 		page_idle_fd = checked_open(SYS_KERNEL_MM_PAGE_IDLE, O_RDWR);
 
 	if (opt_list && opt_pid)