packaging: Fixed building RPMs on non-x86_64 architectures

The DMI decode is available only on the x86_64 architecture, the spec
file was changed to reflect this.

Change-Id: I691544be6630ed2e88acbf8f1828b7995f582ffa
Signed-off-by: Vitor de Lima <vitor.lima@eldorado.org.br>