refactor(measured boot): make measurement strings compliant with SBSG

Made measurement strings compliant to Server Base Security Guide
(SBSG, Arm DEN 0086) hence updated measurement strings for BL32, BL31,
and SCP_BL2 images. As the GPT image is not get measured by BL2 so
removed its measurement string.
Also, namespaced measurement string defines that were looking quite
generic.

Change-Id: Iaa17c0cfeee3d06dc822eff2bd553da23bd99b76
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
3 files changed