build(poetry): install SP dependencies with `--no-root`

Change-Id: I2981cb438be6f4569d069203b555310588db2627
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/Makefile b/Makefile
index e111be2..daab00e 100644
--- a/Makefile
+++ b/Makefile
@@ -1684,7 +1684,7 @@
 # Add Secure Partition packages
 ifeq (${NEED_SP_PKG},yes)
 $(BUILD_PLAT)/sp_gen.mk: ${SP_MK_GEN} ${SP_LAYOUT_FILE} | $$(@D)/
-	$(if $(host-poetry),$(q)poetry -q install)
+	$(if $(host-poetry),$(q)poetry -q install --no-root)
 	$(q)$(if $(host-poetry),poetry run )${PYTHON} "$<" "$@" $(filter-out $<,$^) $(BUILD_PLAT) ${COT} ${SP_DTS_LIST_FRAGMENT}
 sp: $(DTBS) $(BUILD_PLAT)/sp_gen.mk $(SP_PKGS)
 	$(s)echo