Add framework for autheticated decryption of data. Currently this
patch optionally imports mbedtls library as a backend if build option
"DECRYPTION_SUPPORT = aes_gcm" is set to perform authenticated decryption
using AES-GCM algorithm.

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Change-Id: I2966f0e79033151012bf4ffc66f484cd949e7271

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