Was your parakeet using his mouth to scratch his feet? Mine do that a lot, probably to remove dead or flaking skin. The white stuff you are talking about may be just that - dry flaky skin. However, I don' t know what the white stuff is that you are talking about, so he may have some skin condition that you'd want to check with the vet about.
Hopefully its is what like everyone is saying, dry skin. The cold dry air during winter makes this even worse. Before we had a humidifier in our keets room this used to be the case. Not so much with it.