Added SPCI to the glossary

Change-Id: I576ae161477f4a69336d15a7741e566bb103124a
Signed-off-by: Artsem Artsemenka <artsem.artsemenka@arm.com>
diff --git a/docs/global_substitutions.txt b/docs/global_substitutions.txt
index 242e62c..fdca9c3 100644
--- a/docs/global_substitutions.txt
+++ b/docs/global_substitutions.txt
@@ -38,6 +38,7 @@
 .. |SMCCC| replace:: :term:`SMCCC`
 .. |SoC| replace:: :term:`SoC`
 .. |SP| replace:: :term:`SP`
+.. |SPCI| replace:: :term:`SPCI`
 .. |SPD| replace:: :term:`SPD`
 .. |SPM| replace:: :term:`SPM`
 .. |SVE| replace:: :term:`SVE`