i965/device_info: Add a supports_simd16_3src flag

i965/device_info: Add a supports_simd16_3src flag

This also involves moving revision checking to screen creation time and
passing that into brw_get_device_info so that we can get the right
device_info for early versions of SKL.  Since the only place we used
revision was to check for SIMD16 3-src instruction support, it's safe to
remove the revision field from brw_context.

Reviewed-by: Matt Turner <mattst88@gmail.com>