pkg/firmware: Disable firmware packages for s390x

Reduce the number of packages to build for s390x. Firmware
is only used for physical devices, so disable it for s390x
where we mostly run in virtual machines.

Signed-off-by: Rolf Neugebauer <rn@rneugeba.io>

pkg/firmware-all/build.yml

@@ -1,2 +1,5 @@
 image: firmware-all
 network: true
+arches:
+  - amd64
+  - arm64

pkg/firmware/build.yml

@@ -1,2 +1,5 @@
 image: firmware
 network: true
+arches:
+  - amd64
+  - arm64