i965: Set initial kflags on BO creation.

i965: Set initial kflags on BO creation.

This simplifies kflag initialization, by creating a bufmgr-wide setting
for initial kflags, and just applying it whenever we create a new BO.

This also properly allows 48-bit addresses for imported BOs (via prime
or flink), which I had missed in my earlier 48-bit support series.

This will be useful when adding softpin support, as we'll want to add
EXEC_OBJECT_PINNED to initial_kflags as well.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>