drm/i915/selftests: Verify context workarounds

Test context workarounds have been correctly applied in newly created
contexts.

To accomplish this the existing engine_wa_list_verify helper is extended
to take in a context from which reading of the workaround list will be
done.

Context workaround verification is done from the existing subtests, which
have been renamed to reflect they are no longer only about GT and engine
workarounds.

v2:
 * Test after resets and refactor to use intel_context more. (Chris)

v3:
 * Use ce->engine->i915 instead of ce->gem_context->i915. (Chris)
 * gem_engine_iter.idx is engine->id + 1. (Chris)

v4:
 * Make local function static.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190520142546.12493-1-tvrtko.ursulin@linux.intel.com