i965: Don't call abort() on an unknown device.

i965: Don't call abort() on an unknown device.

If we don't recognize the PCI ID, we can't reasonably load the driver.
However, calling abort() is quite rude - it means the application that
tried to initialize us (possibly the X server) can't continue via
fallback paths.  We already have a more polite mechanism - failing to
create the context.  So, just use that.

While we're at it, improve the error message.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=73024
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Tested-by: Lu Hua <huax.lu@intel.com>