I try to set up AMT7-mobo to Admin mode (HostBased with vPro-certificate).
How i can to set PKI DNS suffix without entering in ME (BIOS)? Is it one way - only with DHCP option # 15?
Yes, DHCP option 15 is way to make it happen using PKI.
BTW: you can also use PSK method with a USB key in order to provision the machine in Admin mode without changing DHCP configuration.
No, you can't by OS/programmatically set the sufix DNS in ME due security reasons, but you do it using a USBkey. There a tool in http://software.intel.com/en-us/articles/download-the-latest-intel-amt-software-development-kit-sdk/ AMT SDK called USBFile.exe that allows you create a USB key with Me parameters that you would like to inset into ME.