KVM: x86: Drop vendor specific functions for APICv/AVIC enablement

Now that APICv/AVIC enablement is kept in common 'enable_apicv' variable,
there's no need to call kvm_apicv_init() from vendor specific code.

No functional change intended.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210609150911.1471882c-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>