op-chain-ops: default `L2Addresses` (#3644)

For building a developer genesis, if the `L2Addresses` struct
is `nil`, it will now use the default values. This simplifies
config and reduces code duplication as `nil` can now be passed.
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

op-chain-ops/genesis/layer_two.go

 package genesis
 
 import (
+	"github.com/ethereum-optimism/optimism/op-bindings/predeploys"
 	"github.com/ethereum-optimism/optimism/op-chain-ops/state"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
@@ -29,6 +30,14 @@ func BuildL2DeveloperGenesis(config *DeployConfig, l1StartBlock *types.Block, l2
 	}
 	SetPrecompileBalances(db)
 
+	if l2Addrs == nil {
+		l2Addrs = &L2Addresses{
+			ProxyAdmin:                  predeploys.DevProxyAdminAddr,
+			L1StandardBridgeProxy:       predeploys.DevL1StandardBridgeAddr,
+			L1CrossDomainMessengerProxy: predeploys.DevL1CrossDomainMessengerAddr,
+		}
+	}
+
 	return BuildL2Genesis(db, config, l1StartBlock, l2Addrs)
 }