Add a dedicated standard ID for a SMC fast call for
ARM watchdog service.
Define this ID to 55.

Change-Id: Ifc6962d53912855aaf27afa7c198062d4a2fb4d6
Signed-off-by: Lionel Debieve <lionel.debieve@foss.st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/optee/optee_os/+/289077
Tested-by: Gatien CHEVALLIER <gatien.chevallier@st.com>
Reviewed-by: Gatien CHEVALLIER <gatien.chevallier@st.com>
Domain-Review: Gatien CHEVALLIER <gatien.chevallier@st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/optee/optee_os/+/299715
ACI: CITOOLS <MDG-smet-aci-reviews@list.st.com>