package/nodejs: fix architectural dependencies on ARM

On ARM, starting with v0.12.x, the V8 JS engine is now requires at least
an armv6 and at least a VFPv2.

Since we're about to introduce the v4.x version, which has the same
requirements, introduce an intermediate variable to hold that condition.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Jörg Krause <joerg.krause@embedded.rocks>
Cc: Martin Bark <martin@barkynet.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>