KVM: selftests: Rename KVM_HAS_DEVICE_ATTR helpers for consistency

Rename kvm_device_check_attr() and its variants to kvm_has_device_attr()
to be consistent with the ioctl names and with other helpers in the KVM
selftests framework.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>