drm/i915/panic: fix panic structure allocation memory leak

drm/i915/panic: fix panic structure allocation memory leak

Separating the panic allocation from framebuffer allocation in commit
729c5f7ffa83 ("drm/{i915,xe}/panic: move framebuffer allocation where it
belongs") failed to deallocate the panic structure anywhere.

The fix is two-fold. First, free the panic structure in
intel_user_framebuffer_destroy() in the general case. Second, move the
panic allocation later to intel_framebuffer_init() to not leak the panic
structure in error paths (if any, now or later) between
intel_framebuffer_alloc() and intel_framebuffer_init().

v2: Rebase

Fixes: 729c5f7ffa83 ("drm/{i915,xe}/panic: move framebuffer allocation where it belongs")
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Maarten Lankhorst <dev@lankhorst.se>
Reported-by: Michał Grzelak <michal.grzelak@intel.com>
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Michał Grzelak <michal.grzelak@intel.com> # v1
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://lore.kernel.org/r/20251015095135.2183415-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>