jobs/build-arch: update hack for aarch64/aws serial console

This is an update to the serial console hack added in ddd9da9.
This needed updating because of [1] that will update and
rename gf-platformid to gf-set-platform. Eventually once
platforms.yaml exists everywhere we will finally be able
to drop this patch.

[1] coreos/coreos-assembler#2400

The decoded version of this patch looks like:

```diff
diff --git a/src/gf-set-platform b/src/gf-set-platform
index 3b1c5ae31..df5e0f9d7 100755
--- a/src/gf-set-platform
+++ b/src/gf-set-platform
@@ -59,7 +59,13 @@ blscfg_path=$(coreos_gf glob-expand /boot/loader/entries/ostree-*.conf)
 coreos_gf download "${blscfg_path}" "${tmpd}"/bls.conf
 # Remove any platformid currently there
 sed -i -e 's, ignition.platform.id=[a-zA-Z0-9]*,,g' "${tmpd}"/bls.conf
-sed -i -e '/^options / s,$, ignition.platform.id='"${platformid}"',' "${tmpd}"/bls.conf
+if [ "$(coreos_gf exists /boot/coreos/platforms.json)" != "true" -a "${platformid}" == 'aws' ]; then
+    # Our platform is AWS and we still need the console=ttyS0 hack for the legacy
+    # (no platforms.yaml) path.
+    sed -i -e 's|^\(options .*\)|\1 ignition.platform.id='"${platformid}"' console=ttyS0,115200n8|' "${tmpd}"/bls.conf
+else
+    sed -i -e '/^options / s,$, ignition.platform.id='"${platformid}"',' "${tmpd}"/bls.conf
+fi
 if [ -n "$remove_kargs" ]; then
     # Remove existing qemu-specific kargs
     sed -i -e '/^options / s@ '"${remove_kargs}"'@@' "${tmpd}"/bls.conf

```

jobs/build-arch.Jenkinsfile

@@ -322,7 +322,9 @@ stages:
     - cosa buildextend-openstack
     # Hack for serial console on aarch64 aws images
     # see https://github.com/coreos/fedora-coreos-tracker/issues/920#issuecomment-914334988
-    - echo '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' | base64 --decode | sudo patch /usr/lib/coreos-assembler/gf-platformid
+    # Remove this hack once platforms.yaml exists everywhere
+    # https://github.com/coreos/fedora-coreos-config/pull/1181
+    - echo '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' | base64 --decode | sudo patch /usr/lib/coreos-assembler/gf-set-platform
     - cosa buildextend-aws
   post_commands:
     - cosa compress --compressor xz