buildroot

sam-ba: only propose it if the host is x86 or x86_64

As sam-ba is delivered as a binary for x86

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>