tty: vt: move CSI ECMA handling to a separate function

tty: vt: move CSI ECMA handling to a separate function

Similar to previous moves, move also "CSI ..." (i.e. vc_priv == EPecma)
handling to a separate function.

This is the last large move of code out of do_con_trol(). And despite it
is still 151 lines of code (down from 407!), it is now quite easy to
folllow the transitions of the state machine in there. ESnonstd and
ESpalette handling still can be moved away, but it won't improve that
much.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20240202065608.14019-15-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>