anv: Make entrypoint resolution take a gen_device_info

anv: Make entrypoint resolution take a gen_device_info

In order for things such as the ANV_CALL and the ifuncs to work, we used to
have a singleton gen_device_info structure that got assigned the first time
you create a device.  Given that the driver will never be used
simultaneously on two different generations of hardware, this was fairly
safe to do.  However, it has caused a few hickups and isn't, in general, a
good plan.  Now that the two primary reasons for this singleton are gone,
we can get rid of it and make things quite a bit safer.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>