Bump Linaro platform to 20.01

The CI moved to 20.01, so it needs to be adjusted accordingly.

Change-Id: I197231b0bd52958eb8f5a355551665203096099c
diff --git a/tf-a-builder/builders.sh b/tf-a-builder/builders.sh
index b47f34c..bab1272 100755
--- a/tf-a-builder/builders.sh
+++ b/tf-a-builder/builders.sh
@@ -74,7 +74,7 @@
 install-arm-toolchains
 
 # Additional binaries required (rootfs, etc...)
-LINARO_VERSION=19.06
+LINARO_VERSION=20.01
 mkdir -p \
   ${WORKSPACE}/nfs/downloads/linaro/${LINARO_VERSION} \
   ${WORKSPACE}/nfs/downloads/mbedtls