x86: move dma_map_page and dma_unmap_page to common header

They are similar enough to do this move.
the macro version is ugly, and we use inline functions instead.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>