kvm: Exclude cpuid unit tests on non-X86
kvm: Exclude cpuid unit tests on non-X86

cpuid functions only exist on X86 machines. Don't run their unit tests
on other platforms.

TEST=cd kvm;cargo test --target=aarch64-unknown-linux-gnu
BUG=1112839

Change-Id: I5f7656b41e7143c1833e677669f101a8dead859f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2335448
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Tested-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm