drm/i915/gt: Use i915_vm_put on ppgtt_create error paths

drm/i915/gt: Use i915_vm_put on ppgtt_create error paths

Now that the scratch page and page directories have a reference back to
the i915_address_space, we cannot do an immediate free of the ppgtt upon
error as those buffer objects will perform a later i915_vm_put in their
deferred frees.

The downside is that by replacing the onion unwind along the error
paths, the ppgtt cleanup must handle a partially constructed vm. This
includes ensuring that the vm->cleanup is set prior to the error path.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6900
Signed-off-by: Chris Wilson <chris.p.wilson@intel.com>
Fixes: 4d8151ae5329 ("drm/i915: Don't free shared locks while shared")
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: <stable@vger.kernel.org> # v5.14+
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220926153333.102195-1-matthew.auld@intel.com