Include x509.h header file explicitly. Update docs.

Change-Id: If2e52c2cd3056654406b7b6779b67eea5cc04a48
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>

Add the support needed to enable using CryptoCell integration with
with RSA 3K support.

Signed-off-by: Gilad Ben-Yossef <gilad.benyossef@arm.com>
Change-Id: I95527cb0c41ae012109e8968dd20a4ae9fe67f17

Add support for multiple Cryptocell revisions which
use different APIs.

This commit only refactors the existing code in preperation to the addition
of another Cryptocell revisions later on.

Signed-off-by: Gilad Ben-Yossef <gilad.benyossef@arm.com>
Change-Id: I16d80b31afb6edd56dc645fee5ea619cc74f09b6