tty: vt: make vtconsole_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/2023100546-humbly-prologue-e58c@gregkh


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