Earlier I was using my RaspberryPi with Waveshare LCD and Raspbian was installed so there was no issue with display, but now I have Android T
As of now Android Things image isn't shipped with a default configuration for display in config.txt file which is located in the root of your SD card (see the boot partition). The configuration should be added manually. Look for an appropriate display configuration in the supplied documentation or manufacturer's website.
For example, in my case for Waveshare 5inch 800x480 HDMI LCD (B) the following lines needed to be appended to config.txt:
max_usb_current=1
hdmi_group=2
hdmi_mode=87
hdmi_cvt 800 480 60 6 0 0 0
In fact, the max_usb_current, hdmi_group and hdmi_mode parameters with the values above should work for a wide range of displays from different manufacturers. Screen resolution in hdmi_cvt will vary.