mkosi: Include fewer modules in the initramfs

Let's only use mkosi's default list of modules instead of all of
them.

mkosi.conf

@@ -43,6 +43,9 @@ KernelCommandLine=systemd.crash_shell
                   systemd.mask=isc-dhcp-server.service
                   systemd.mask=mdmonitor.service
 
+KernelModulesInitrdExclude=.*
+KernelModulesInitrdInclude=default
+
 [Host]
 Credentials=journal.storage=persistent
 @Incremental=yes