ahci: support the STA2X11 I/O Hub

The AHCI controller found in the STA2X11 chip uses BAR number 0
instead of 5. Also, the chip's fixup code sets a special DMA mask
for all of its PCI functions, and the mask must be preserved here.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Giancarlo Asnaghi <giancarlo.asnaghi@st.com>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>