tty: vt: define an enum for CSI+m codes

It's always confusing to read all those case 0:, case 1: etc. in csi_*
handlers. Define enum entries for all those constants in CSI+m and use
them in csi_m().

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Tested-by: Helge Deller <deller@gmx.de> # parisc STI console
Link: https://lore.kernel.org/r/20240122110401.7289-10-jirislaby@kernel.org


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