openssl: fix architecture specified when configuring openssl

This patch will default to linux-generic32, unless a known optimized
architecture is selected.

As of today it will select optimized config for; avr32, ia64, powerpc and
x86_64.

This fixes bug #5344.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>