char: xillybus: make xillybus_class a static const structure

char: xillybus: make xillybus_class a static const structure

Now that the driver core allows for struct class to be in read-only
memory, move the xillybus_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at load time.

Cc: Eli Billauer <eli.billauer@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Acked-by: Eli Billauer <eli.billauer@gmail.com>
Link: https://lore.kernel.org/r/20230620143751.578239-18-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>