Technically, the answer is none. In reality, the answer is a bit more complicated. PTT is a feature implemented in the Management Engine (ME), which is built into the chipset. There exist, however, a great many processors that come as System on a Chip (SoC) packages that include both processor and chipset. Support was included starting in 4th gen systems that used SoC packages. Practically all SoC packages for 5th gen and later processors included PTT, as did the corresponding versions of the chipsets for Desktop, etc.
Now, it is important to say that whether a particular motherboard or system has PTT support is dependent upon the appropriate firmware being included, both in the ME and in the BIOS.
Hope this helps,