libckteec: add support for Signing and Verification Functions

Adds support for following API's :
- C_SignInit()
- C_Sign()
- C_SignUpdate()
- C_SignFinal()
- C_VerifyInit()
- C_Verify()
- C_VerifyUpdate()
- C_VerifyFinal()

Co-developed-by: Etienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: Ruchika Gupta <ruchika.gupta@linaro.org>
Reviewed-by: Ricardo Salveti <ricardo@foundries.io>