i965: add a kernel_features bitfield to intel screen

i965: add a kernel_features bitfield to intel screen

We can use this to track various features that may or may not be supported
by the hw / kernel. Currently, we usually do this by checking the generation
and supported command parser versions in various places thoughtout the driver
code. With this patch, we centralize all these checks in just once place at
screen creation time, then we just query the bitfield wherever we need to
check if a particular feature is supported.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>