libckteec: serialize_ck.c: serialize AES-GCM mechanism parameters

This commits adds serialize_mecha_aes_gcm() function to serialize_ck.c
to support AES-GCM mechanism (CKM_AES_GCM) in libckteec.

Co-developed-by: Etienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: Marouene Boubakri <marouene.boubakri@nxp.com>
Reviewed-by: Etienne Carriere <etienne.carriere@foss.st.com>