chore: support building Fedora on arm64 AKA aarch64

By default [1] the `aarch64` ARCH value is converted to `arm64`. But
Fedora uses `aarch64` to refer to the architecture.

Convert incoming ARCH values of `arm64` into `aarch64` as is already
done for `amd64` -> `x86_64`

[1] 174089a6a5/diskimage_builder/lib/common-defaults (L29-L30)

Change-Id: I6d9698e45b1183007bac49544da196ec78a7ac6a

diskimage_builder/elements/fedora/root.d/10-fedora-cloud-image

@@ -12,6 +12,9 @@ set -o pipefail
 if [ 'amd64' = "$ARCH" ] ; then
     ARCH="x86_64"
 fi
+if [[ "${ARCH}" == "arm64" ]]; then
+    ARCH="aarch64"
+fi
 
 DIB_LOCAL_IMAGE=${DIB_LOCAL_IMAGE:-""}