platform/x86: make fw_attr_class constant

Since commit 43a7206b0963 ("driver core: class: make class_register() take
a const *"), the driver core allows for struct class to be in read-only
memory, so move the fw_attr_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at boot time.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Ricardo B. Marliere" <ricardo@marliere.net>
Link: https://lore.kernel.org/r/20240305-class_cleanup-platform-v1-1-9085c97b9355@marliere.net
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

platform/x86: firmware_attributes_class: Create helper file for handling firmware-attributes class registration events

This offers shared code for registering the firmware_attributes_class,
which is used by the Dell and Lenovo WMI management drivers.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Mark Pearson <markpearson@lenovo.com>
Link: https://lore.kernel.org/r/20210530223111.25929-1-markpearson@lenovo.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>