setools: Add missing bison dependency

The setools package needs the yacc utility which is part of the bison
package to build.

Fixes http://autobuild.buildroot.net/results/8f9/8f95e83411552397ca29e9aee5c457a1a762b364/



Signed-off-by: Clayton Shotwell <clayton.shotwell@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>