drm/i915: Make ring submission compatible with obj->mm.lock removal, v2.

We map the initial context during first pin.

This allows us to remove pin_map from state allocation, which saves
us a few retry loops. We won't need this until first pin anyway.

intel_ring_submission_setup() is also reworked slightly to do all
pinning in a single ww loop.

Changes since v1:
- Handle -EDEADLK backoff in intel_ring_submission_setup() better.
- Handle smatch errors reported by Dan and testbot.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-20-maarten.lankhorst@linux.intel.com