tests: make pesign optional requirement for kernel rebuild

tests/Sanity/rebuild-kernel-and-reboot/main.fmf

@@ -51,16 +51,13 @@ require:
 - xmlto
 - asciidoc
 - net-tools
-- pesign
 duration: 20h
 
-#adjust:
-#  - because: "C9S-specific requirements"
-#    when: distro == c9s
-#    require+:
-#      - ppl-devel
-#      - cloog-ppl-devel
-#      - gcc-java
+adjust:
+  - because: "pesign is available for some architectures only"
+    when: distro == rhel and arch != ppc64le and arch != s390x
+    require+:
+      - pesign
 
 # Dropping TCMS integration, these links should not be needed anymore.
 # extra-summary: /tools/binutils/Sanity/rebuild-kernel-and-reboot