gem5: update to 08c79a194d1a3430801c04f37d13216cc9ec1da3

Fix gem5 userland fatal: kernel too old.

Fix https://github.com/cirosantilli/linux-kernel-module-cheat/issues/64
gem5 x86 boot fails with: "Assertion `locked && curr_frag_id == 0' failed

So we are now back to mainline gem5!

run

@@ -458,6 +458,7 @@ Extra options to append at the end of the emulator command line.
                 cmd.extend([
                     self.env['gem5_se_file'], LF,
                     '--cmd', self.env['image'], LF,
+                    '--param', 'system.cpu[:].workload[:].release = "{}"'.format(self.env['kernel_version']), LF,
                 ])
                 if self.env['userland_args'] is not None:
                     cmd.extend(['--options', self.env['userland_args'], LF])