drm/i915: Skip error capture when wedged on init

Trying to capture uninitialised engines when we wedged on init ends in
tears. Skip that together with uC capture, since failure to initialise the
latter can actually be one of the reasons for wedging on init.

v2:
 * Use i915_disable_error_state when wedging on init/fini.

v3:
 * Handle mock tests.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com> # v1
Link: https://patchwork.freedesktop.org/patch/msgid/20211111130634.266098-1-tvrtko.ursulin@linux.intel.com