drm/i915/selftests: allow misaligned_pin test work with unmappable memory

In case of Small BAR configurations stolen local memory can be unmappable.
Since the test does not touch the memory, passing I915_BO_ALLOC_GPU_ONLY
flag to i915_gem_object_create_region, will prevent -ENOSPC error from
_i915_gem_object_stolen_init.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6565


Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220825154239.52343-1-andrzej.hajda@intel.com