To add report server content types
1.Open the library for which you want to add Reporting Services content types.
2.On the Library Tools ribbon tabs, click the Library tab.
3.On the Settings ribbon group, click Library Settings.
4.Under Content Types, click Add from existing site content types.
5.In the Select Content Types section, in Select site content types from, click the arrow to select Reporting Services. << This should actually say ‘SQL Server Reporting Services Content Types. Please see the image below:
7.To add Report Model and Report Data Source content types, repeat steps 5 and 6.
8.When you finish selecting all of the content types that you want to add, click OK.
I hope that helps someone out.