iar-docker-images: Add 9.50.2 support

Signed-off-by: Arthur She <arthur.she@linaro.org>
Change-Id: I1c136fa4414b720459b9ac31f5d6e736bbb7fdce
diff --git a/iar-docker-images.yaml b/iar-docker-images.yaml
index 4de7470..b9b040d 100644
--- a/iar-docker-images.yaml
+++ b/iar-docker-images.yaml
@@ -27,6 +27,11 @@
         - string:
             name: GERRIT_REFSPEC
             default: ''
+        - string:
+            name: IAR_PACKAGE
+            default: 'bxarm-9.50.2.deb'
+            description: |
+              IAR toolchain install package file name
     wrappers:
     - timestamps
     - timeout: