x86/pci-dma: remove the experimental forcesac boot option

Limiting the dma mask to avoid PCI (pre-PCIe) DAC cycles while paying
the huge overhead of an IOMMU is rather pointless, and this seriously
gets in the way of dma mapping work.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>