libdrm: Fix PCI domain domain support

This works in conjunction with newer kernels. If we succeed in requesting
interface 1.4, the we know the kernel provides proper domain numbers. If
not, ignore the domain number as it's bogus (except on Alpha).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Adam Jackson <ajax@redhat.com>