tools/vm: Switch to liblk library

page-flags.c had some older version of debugfs_mount copied from perf so
convert it to using the version in the tools library.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Link: http://lkml.kernel.org/r/1361374353-30385-8-git-send-email-bp@alien8.de


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>