If you with to run at 100 MHz, set the clock constrain in the .SDC to 10 ns and then synthesize the design again.
Assuming it will fail to meet that constrain, then one option is to change the synthesis and fitting settings for speed and try again.
If it still fails, you need to track down the critical paths.
If you find the critical path is related to a slave, you can consider using a dual clock bridge to run that clock at a lower frequency.
If you find the critical path is related to the Avalon fabric itself, then:
a) do you have unnecessary master-slave connections in your bus?
b) consider using pipeline or dual clock bridges to reduce the complexity.
In order to use bridged, you need to place a bridge in your SOPC.
The bridge will have a master and a slave port.
Connect your masters to the bridge's slave port.
Connect the bridge's master port to the slaves you want to place under the bridge.