All the psychiatry programs I know of are 4-year programs, where the internship (which includes variable months of medicine, neuro, and psychiatry) is all included in the categorical application. You don't need to apply to a prelim year. This used to be different in the past, and some places did have a prelim year, but currently, I don't know any programs where you need a prelim year.
Of course, if you have already done a year of internship (in another specialty, for example), you can apply for a PGY-2 advanced spot available at some programs where you would complete the last three years of adult psychiatry. This is mostly for people who switch between programs or from other specialties (not what you would apply for directly out of med school).
If you apply to a combined adult/child psychiatry track, at many schools, you match for a 5-year categorical program (at most places, this includes peds internship and 2 years of child fellowship, so you do not complete the fourth year of adult psych residency).