distro: take architecture as an argument

Allow bootloader specific packages to be defined per architecture,
and allow repositories to depend on the architecture.

This does not altert he pipelines we produce, part from the ami
image now contains the grub2-pc package, rather than the grub2
package. This should make no difference.

Signed-off-by: Tom Gundersen <teg@jklm.no>

test/cases/rhel82_ami.json

@@ -77,7 +77,7 @@
             "dhcp-client",
             "dracut-config-generic",
             "gdisk",
-            "grub2",
+            "grub2-pc",
             "insights-client",
             "kernel",
             "langpacks-en",