Fix GetTPMv2Signer function signature in Windows file

* Rename platform-specific files to be consistent in format

Author: 13ajay

…gning_helper/darwin_cert_store_signer.go …gning_helper/cert_store_signer_darwin.goaws_signing_helper/darwin_cert_store_signer.go renamed to aws_signing_helper/cert_store_signer_darwin.go aws_signing_helper/darwin_cert_store_signer.go renamed to aws_signing_helper/cert_store_signer_darwin.go

@@ -6,6 +6,6 @@ import (
 	"errors"
 )
 
-func GetTPMv2Signer(certIdentifier CertIdentifier) (signer Signer, signingAlgorithm string, err error) {
+func GetTPMv2Signer(opts GetTPMv2SignerOpts) (signer Signer, signingAlgorithm string, err error) {
 	return nil, "", errors.New("unable to use tpm v2 signer on windows")
 }