x86: move tracedata to RODATA

.. allowing it to be write-protected just as other read-only data
under CONFIG_DEBUG_RODATA.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>