valgrind: enable tls support

Tested with example program from [1] with qemu_x86_64.

[1] http://valgrind.10908.n7.nabble.com/Thread-local-storage-TLS-support-td40815.html



Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>