[Intel-gfx] [PATCH v2, 0/4] improve handling of the driver's default context

[Dave Gordon]

A reworking of the previous patchset, incorporating Daniel Vetter's
point that we don't need intel_context::file_priv and Chris Wilson's
wish to abolish engine::default_context.

Patch 1/4 starts the process by eliminating file_priv, which was only used
in one place. Patch 2/4 removes lots of references to default_context,
wherever it was used in a comparison. Patch 3/4 continues by removing
more references to default_context, wherever it was used for allocation.
And at the last, patch 4/4 replaces the remaining per-engine uses with a
single per-device pointer, thus finally making the refcounting sane.

Enjoy :)