KVM: x86: Use KBUILD_MODNAME to specify vendor module name

Use KBUILD_MODNAME to specify the vendor module name instead of manually
writing out the name to make it a bit more obvious that the name isn't
completely arbitrary.  A future patch will also use KBUILD_MODNAME to
define pr_fmt, at which point using KBUILD_MODNAME for kvm_x86_ops.name
further reinforces the intended usage of kvm_x86_ops.name.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221130230934.1014142-34-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>