KVM: nSVM: remove HF_VINTR_MASK

Now that the int_ctl field is stored in svm->nested.ctl.int_ctl, we can
use it instead of vcpu->arch.hflags to check whether L2 is running
in V_INTR_MASKING mode.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>