drm/i915: Record the sseu configuration per-context & engine

We want to expose the ability to reconfigure the slices, subslice and
eu per context and per engine. To facilitate that, store the current
configuration on the context for each engine, which is initially set
to the device default upon creation.

v2: record sseu configuration per context & engine (Chris)

v3: introduce the i915_gem_context_sseu to store powergating
    programming, sseu_dev_info has grown quite a bit (Lionel)

v4: rename i915_gem_sseu into intel_sseu (Chris)
    use to_intel_context() (Chris)

v5: More to_intel_context() (Tvrtko)
    Switch intel_sseu from union to struct (Tvrtko)
    Move context default sseu in existing loop (Chris)

v6: s/intel_sseu_from_device_sseu/intel_device_default_sseu/ (Tvrtko)

Tvrtko Ursulin:

v7:
 * Pass intel_sseu by pointer instead of value to make_rpcs.
 * Rebase for make_rpcs changes.

v8:
 * Rebase for RPCS edit on pin.

v9:
 * Rebase for context image setup changes.

v10:
 * Rename dev_priv to i915. (Chris Wilson)

v11:
 * Rebase.

v12:
 * Rebase for IS_GEN changes.

v13:
 * Rebase for RUNTIME_INFO.

v14:
 * Rebase for intel_context_init.

v15:
 * Rebase for drm-tip changes.

v16:
 * Moved struct intel_sseu definition to i915_gem_context.h.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190205095032.22673-1-tvrtko.ursulin@linux.intel.com