x86: no CPA on iounmap

When an ioremap is unmapped, do not change the page attributes. There might
be another mapping of the same physical address. PAT might detect a conflicting
mapping attribute for no good reason. The mapping is removed anyway.

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