tty: vc_screen: make vc_class constant

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

Cc: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/2023100549-sixth-anger-ac34@gregkh


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