kvm-unit-tests: pass the --processor configure argument

kvm-unit-tests: pass the --processor configure argument

The configure script uses this to set the -mcpu option. If nothing is
passed, it defaults to -mcpu=cortex-a15 for arm, and -mcpu=cortex-a57
for aarch64, which may conflict with the actual architecture.

The --processor option is only really used for arm and aarch64, but it
doesn't hurt to also pass it for the other arches.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>