drm/i915: Drop new chunks of context creation ABI (for now)

drm/i915: Drop new chunks of context creation ABI (for now)

The intent was to expose these as part of the means to perform full
context recovery (though not the SINGLE_TIMELINE, that is for later and
just sucked as collateral damage). As that requires a couple more
patches to complete the series, roll back the earlier chunks of ABI for
an intervening PR. We keep all the internals intact and under selftests.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190327105814.14694-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>