nodejs: not supported on old ARM cores

nodejs needs the ARM blx instruction which is only supported in v5t+
cores (v5 ISA with thumb instructions).
Disable it for lower cores. Fixes:
http://autobuild.buildroot.net/results/89e/89ee5ba047a26a8c7a612d0285b08780b70efbd4/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>