auth: tbbr: move firmware configuration into common part

Move the fw_config authentication structure into the common part.
Without BL1, the fw_config will be added into the BL2 firmware.
It will be loaded from FIP and authenticated in BL2.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: I3b8f8e99961d28d3d15a6dbff06b0d9cdda20881
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/184832


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: Nicolas TOROMANOFF <nicolas.toromanoff@st.com>
Reviewed-by: CIBUILD <smet-aci-builds@lists.codex.cro.st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>
Tested-by: Nicolas TOROMANOFF <nicolas.toromanoff@st.com>