Correction: After further analysis of VoLTE ompatibility with SOCs, i have compiled a list:
It includes these Snapdragon chipsets:- 210, 400, 410, 415, 425, 430, 435, 615, 616, 617, 625, 650, 652, 800, 801, 805, 808, 810, 820, 821 and 823.
These are list for Mediatek once :- MT6752, MT6753, MT6755 (a.k.a. Helio p10), MT6795 (a.k.a. Helio x10), MT6797 (a.k.a. Helio x20), MT6757 (a.k.a. Helio p20).
though many other too support VoLTE but the above mentioned are the most commonly available in the market. Also to enble it on LTE devices Microsoft has to push for an firmware update.