drm/{i915,xe}/panic: split out intel_panic.[ch]

intel_bo.[ch] is not the appropriate location for the panic
functionality. Split out intel_panic.[ch] and xe_panic.c in i915 and
xe. Keep the function names for now.

Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Maarten Lankhorst <dev@lankhorst.se>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://lore.kernel.org/r/d98b831a011a028ffd33ce99b0ba62be061ee235.1756835342.git.jani.nikula@intel.com