wireguard: selftests: enable ACPI for SMP

It turns out that by having CONFIG_ACPI=n, we've been failing to boot
additional CPUs, and so these systems were functionally UP. The code
bloat is unfortunate for build times, but I don't see an alternative. So
this commit sets CONFIG_ACPI=y for x86_64 and i686 configs.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>