Hello!
I have exactly the same problem with my SCCM 2012 SP1 server. The problem started before I have had installed SP1. Trying to fix issue I have installed SP1 over existing installation, but no luck nor visible progress.
ReportingServicesService.exe is eating my servers cpu. Spike starts every minute then goes down for a minute and start over again after one minute. I will post some explaining screenshots below.
I am not SQL experts. For me it looks like SCCM is running some reports enumerations tasks every minute.
srsrp.log:
ReportServerService.log
srsrp.log
ReportServerService.log