[Intel-gfx] Premature unpinning at last

[Chris Wilson]

Pulled in the few missing details to put everything together in the same
series. Still missing a few r-b through:

[02/19] io-mapping: Specify mapping size for
[05/19] drm/i915: Use i915_vma_pin_iomap on the ringbuffer
[10/19] drm/i915: Rearrange switch_context to load the aliasing
[14/19] drm/i915: Move context initialisation to first-use
[17/19] drm/i915: Track the previous pinned context inside the

02/19 requires an external ack (or Daniel's blessing), but it would
still be good for one of us to r-b it.

Hopefully CI is happy as well,
-Chris