In order to use the "Package Device Material Breakdowns" you need to know the package type for your device which can be determined from the complete part number and the "Part Number description" section of the data sheet. For example, if the part number is ispLSI2064VE-280LT100, the package type is a 100 pin TQFP (not lead-free). Then you can find the Leaded, 100 pin TQFP document on the web site to check which materials it contains.
Another document that is available is the "Information Regarding Chemical Substances in LSC Products and Packaging". This is also available on the same page as the "Package Device Material Breakdowns". This document contains a list of the materials that are not added to the Lattice devices intentionally. If you open this document you will see that Beryllium is on the list of materials which are not intentionally added to Lattice devices. From this you can conclude that the ispLSI2064VE will not contain Beryllium.