x86: move initialization functions to pci-dma.c

initcalls that triggers the various possibiities for
dma subsys are moved to pci-dma.c.

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