non-PCI driver name lookup

[Robert Swindells <rjs%fdy2.co.uk@localhost>]

The pinebook uses the modesetting X11 driver.

An application that calls DRI2Connect() doesn't get back valid values
for device name and driver name so typically assumes that DRI2 isn't
available.

This looks to be down to how libdrm tries to work out which driver is
being used from an open file descriptor. I presume the NetBSD specific
code in it does work for PCI devices but it looks like we need to add
something for display devices that are built into the CPU.