Tweak requires of kernel rebuild for RHEL-8

tests/rebuilds/kernel/main.fmf

@@ -29,7 +29,6 @@ require+:
   - rng-tools
   - newt-devel
   - perl-ExtUtils-Embed
-  - unifdef
   - elfutils-libelf-devel
   - elfutils-devel
   - pciutils-devel
@@ -39,7 +38,6 @@ require+:
   - glibc-static
   - texinfo
   - gdb
-  - ecj
   - graphviz
   - gmp-devel
   - mpfr-devel
@@ -54,12 +52,12 @@ adjust+:
         KERNEL: kernel-core
 
   - because: "python-devel has different names in different distros"
-    when: distro == rhel-8.9
+    when: distro >= rhel-8.6 and distro <= rhel-8.9
     require+:
       - python3-devel
 
   - because: "python-devel has different names in different distros"
-    when: distro != rhel-8.9
+    when: distro < rhel-8.6 and distro > rhel-8.9
     require+:
       - python-devel
 
@@ -68,6 +66,16 @@ adjust+:
     require+:
       - pesign
 
+  - because: "unifdef is available with RHEL-8.9 and newer"
+    when: distro >= rhel-8.9
+    require+:
+      - unifdef
+
+  - because: "ecj is available with RHEL-8.8 and newer"
+    when: distro >= rhel-8.8
+    require+:
+      - ecj
+
   - because: "kernel rebuild fails because of discovering build issues"
     when: collection == gcc-toolset-13
     enabled: false