x86: switch direct mapping setup over to set_pte

Use set_pte() for setting up the 2MB pages in the direct mapping.

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