Add KVM symbols for older kernels.

This patch fixes these build errors on 3.4 and older.

  CC	ioctls/kvm.o
ioctls/kvm.c:21:2: error: ‘KVM_S390_UCAS_MAP’ undeclared here (not in a function)
ioctls/kvm.c:22:2: error: ‘KVM_S390_UCAS_UNMAP’ undeclared here (not in a function)
ioctls/kvm.c:23:2: error: ‘KVM_S390_VCPU_FAULT’ undeclared here (not in a function)
ioctls/kvm.c:55:2: error: ‘KVM_ASSIGN_SET_INTX_MASK’ undeclared here (not in a function)
ioctls/kvm.c:56:2: error: ‘KVM_SIGNAL_MSI’ undeclared here (not in a function)
ioctls/kvm.c:114:2: error: ‘KVM_DIRTY_TLB’ undeclared here (not in a function)
ioctls/kvm.c:115:2: error: ‘KVM_GET_ONE_REG’ undeclared here (not in a function)
ioctls/kvm.c:116:2: error: ‘KVM_SET_ONE_REG’ undeclared here (not in a function)
ioctls/kvm.c:117:2: error: ‘KVM_KVMCLOCK_CTRL’ undeclared here (not in a function)
make: *** [ioctls/kvm.o] Error 1

Signed-off-by: Vinson Lee <vlee@twitter.com>