x86: make sure initmem is writable

When we free initmem, various rodata and CPA checks may have left
memory read only.. this patch ensures that the memory is writable
before we free it.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>