sysfs/cpu: Make crash_hotplug attribute world-readable

sysfs/cpu: Make crash_hotplug attribute world-readable

There is no reason to restrict access to this attribute, as it merely
reports whether crash elfcorehdr is automatically updated on CPU hot
plug/unplug and/or online/offline events.

Note that since commit 79365026f8694 ("crash: add a new kexec flag for
hotplug support"), this maps to the same flag which is world-accessible
through /sys/devices/system/memory/crash_hotplug.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>
Acked-by: Baoquan He <bhe@redhat.com>
Acked-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Link: https://lore.kernel.org/r/20240711103409.319673-1-petr.tesarik@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>