Commit a8eb286 introduced the
following error when creating ECDSA certificates.
ERROR: Error creating key 'Trusted World key'
Makefile:634: recipe for target 'certificates' failed
make: *** [certificates] Error 1
this patch adds the function to create PKCS#1 v1.5.
Change-Id: Ief96d55969d5e9877aeb528c6bb503b560563537
Signed-off-by: Qixiang Xu <qixiang.xu@arm.com>