cxl: make cxl_class constant

Now that the driver core allows for struct class to be in read-only
memory, we should make all 'class' structures declared at build time
placing them into read-only memory, instead of having to be dynamically
allocated at runtime.

Cc: Andrew Donnellan <ajd@linux.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linuxppc-dev@lists.ozlabs.org
Acked-by: Frederic Barrat <fbarrat@linux.ibm.com>
Link: https://lore.kernel.org/r/2023102434-haiku-uphill-0c11@gregkh


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>