How to migrate SSAS and SSRS from SQL Server 2008R2 to SQL Server 2012?
Unless you have data in your SSAS cubes that no longer exists in your source (if this is the case correct that going forward!) then you can simply install a new instance of SSAS then deploy and process your SSAS solutions from SSDT (the 2012+ replacement for BIDS).

For SSRS if you have a basic install you can do the same thing - simply install the new server and deploy your reports. If you have a lot of reports, folders, security setup, schedules etc. then you should migrate.

Here are the MSDN Documents outlining the steps to migrate and the considerations prior to doing so.