Use system variable for ECR repository

ECR repositories are stored in system variables. Use this
so that CI can work parellly to the one in upstream.

Change-Id: Id75bb5a49305a7abc059741f8bcb4e60595fbf1a
Signed-off-by: Saheer Babu <saheer.babu@arm.com>
diff --git a/iar-docker-images/builders.sh b/iar-docker-images/builders.sh
index aa68454..c212cdd 100755
--- a/iar-docker-images/builders.sh
+++ b/iar-docker-images/builders.sh
@@ -16,14 +16,14 @@
 fi
 
 aws configure list
-ECR=987685672616.dkr.ecr.us-east-1.amazonaws.com
-export IAR_ECR=987685672616.dkr.ecr.us-east-1.amazonaws.com/iar
+export ECR=${PRIVATE_CONTAINER_REGISTRY}
+export IAR_ECR=${PRIVATE_CONTAINER_REGISTRY}/iar
 # Get armclang toolchain
 aws s3 cp --recursive s3://openci-trustedfirmware-private-${INFRA_ENV}/armclang/ .
 # Get IAR toolchain binary
 aws s3 cp --recursive s3://openci-trustedfirmware-iar-${INFRA_ENV}/ .
 find .
-aws ecr get-login-password --region us-east-1|docker login --username AWS --password-stdin $ECR
+aws ecr get-login-password --region eu-west-1|docker login --username AWS --password-stdin $ECR
 
 image=$(dirname $(find . -name build.sh))
 test -d $image  && test -f $image/build.sh && \