KVM: VMX: Call vmx_get_cpl() directly in handle_dr()

Use vmx_get_cpl() instead of bouncing through kvm_x86_ops.get_cpl() when
performing a CPL check on MOV DR accesses.  This avoids a RETPOLINE (when
enabled), and more importantly removes a vendor reference to kvm_x86_ops
and helps pave the way for unexporting kvm_x86_ops.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220128005208.4008533-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>