KVM: selftests: Add a helper to read kvm boolean module parameters

Add a helper function for reading kvm boolean module parameters values.
No functional change intended.

Signed-off-by: Like Xu <likexu@tencent.com>
Link: https://lore.kernel.org/r/20230214084920.59787-2-likexu@tencent.com


Signed-off-by: Sean Christopherson <seanjc@google.com>