Support parameter update in fp32
Support parameter update in fp32

hvy/chainer,keisuke-umezawa/chainer,chainer/chainer,rezoo/chainer,niboshi/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,okuta/chainer,aonotas/chainer,jnishi/chainer,wkentaro/chainer,okuta/chainer,ronekko/chainer,hvy/chainer,ktnyt/chainer,okuta/chainer,ktnyt/chainer,hvy/chainer,anaruse/chainer,chainer/chainer,pfnet/chainer,keisuke-umezawa/chainer,hvy/chainer,wkentaro/chainer,chainer/chainer,niboshi/chainer,chainer/chainer,niboshi/chainer,jnishi/chainer,tkerola/chainer,okuta/chainer,jnishi/chainer,niboshi/chainer,ktnyt/chainer,wkentaro/chainer,ktnyt/chainer,wkentaro/chainer,jnishi/chainer