drm/i915/selftests: Context SSEU reconfiguration tests

Exercise the context image reconfiguration logic for idle and busy
contexts, with the resets thrown into the mix as well.

Free from the uAPI restrictions this test runs on all Gen9+ platforms
with slice power gating.

v2:
 * Rename some helpers for clarity.
 * Include subtest names in error logs.
 * Remove unnecessary function export.

v3:
 * Rebase for RUNTIME_INFO.

v4:
 * Fix incomplete unexport from v2. (Chris Wilson)

v5:
 * Rebased for runtime pm api changes.

v6:
 * Rebased for i915_reset.c.

v7:
 * Tidy checkpatch warnings.
 * Consolidate error checking and logging a bit.
 * Skip idle test phase if something failed before it.

v8:
 (Chris Wilson)
 * Fix i915_request_wait error handling.
 * No need to PIN_HIGH the VMA.
 * Remove pointless GEM_BUG_ON before pointer dereference.

v9:
 * Avoid rq leak if rpcs query fails. (Chris)

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> # v6
Link: https://patchwork.freedesktop.org/patch/msgid/20190205095032.22673-5-tvrtko.ursulin@linux.intel.com