valgrind: bump to 3.6.1 and add support for ARMv7

We removed the shell script that wrapped valgrind (not nice to install
such non-standard things), and will let the user use the uclibc.supp
suppression file if needed.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>