tools vm: Fix build due to removal of tools/lib/api/fs/debugfs.h

There were some changes in how this debugfs mounting helper is
implemented/exported and we forgot to check if there were other users
besides perf, fix it.

Need to do a make -C tools/ everytime we do changes to
tools/{lib,include} and other places where we're moving things from
tools/perf/ to be used by other tools/ living code.

Fixed:

  $ make -C tools/vm
  make: Entering directory '/home/git/linux/tools/vm'
  make -C ../lib/api
  make[1]: Entering directory '/home/git/linux/tools/lib/api'
    CC       fd/array.o
    LD       fd/libapi-in.o
    CC       fs/fs.o
    CC       fs/tracing_path.o
    LD       fs/libapi-in.o
    CC       cpu.o
    LD       libapi-in.o
    AR       libapi.a
  make[1]: Leaving directory '/home/git/linux/tools/lib/api'
  gcc -Wall -Wextra -I../lib/ -o page-types page-types.c ../lib/api/libapi.a
  make: Leaving directory '/home/git/linux/tools/vm'
  $
Reported-by: Vinson Lee <vlee@twopensource.com>
Tested-by: Vins...

tools/vm/page-types.c

@@ -42,7 +42,7 @@
 #include <sys/mman.h>
 #include "../../include/uapi/linux/magic.h"
 #include "../../include/uapi/linux/kernel-page-flags.h"
-#include <api/fs/debugfs.h>
+#include <api/fs/fs.h>
 
 #ifndef MAX_PATH
 # define MAX_PATH 256
@@ -188,7 +188,7 @@ static int		kpageflags_fd;
 static int		opt_hwpoison;
 static int		opt_unpoison;
 
-static char		*hwpoison_debug_fs;
+static const char	*hwpoison_debug_fs;
 static int		hwpoison_inject_fd;
 static int		hwpoison_forget_fd;
 
@@ -487,7 +487,7 @@ static void prepare_hwpoison_fd(void)
 {
 	char buf[MAX_PATH + 1];
 
-	hwpoison_debug_fs = debugfs_mount(NULL);
+	hwpoison_debug_fs = debugfs__mount();
 	if (!hwpoison_debug_fs) {
 		perror("mount debugfs");
 		exit(EXIT_FAILURE);