No, the AP3912i ports (P1, P2, P3) do not support 802.1x at this time.
Latest update from release notes:
Enhancements in 10.21.02.0017
wns0016943 Enable support for MAC Based authentication and Captive Portal on AP3912i wired ports.
Note: Support for 802.1x on the port will be provided into a later release.