enable parallel xz compression of modules

So this uses the -P option for xargs to allow parallel compression
of xz uaing xargs options, it allows maximum usage of available CPUs
it can be reverted to the prior status quo but running the following
sed -i 's/global zcpu `nproc --all`/global zcpu 1/' kernel.spec

kernel.spec

@@ -22,6 +22,8 @@ Summary: The Linux kernel
 
 %if %{zipmodules}
 %global zipsed -e 's/\.ko$/\.ko.xz/'
+# for parallel xz processes, replace with 1 to go back to single process
+%global zcpu `nproc --all`
 %endif
 
 # define buildid .local
@@ -1559,7 +1561,7 @@ BuildKernel %make_target %kernel_image %{_use_vdso}
     fi \
   fi \
   if [ "%{zipmodules}" -eq "1" ]; then \
-    find $RPM_BUILD_ROOT/lib/modules/ -type f -name '*.ko' | xargs xz; \
+    find $RPM_BUILD_ROOT/lib/modules/ -type f -name '*.ko' | xargs -P%{zcpu} xz; \
   fi \
 %{nil}