(syms_of_keyboard): Move DEFVAR_DISPLAY's here from callint.c.

(syms_of_keyboard): Move DEFVAR_DISPLAY's here from callint.c.
[MULTI_PERDISPLAY] (current_perdisplay): New var.
(find_active_event_queue): Search all perdisplays.
(init_perdisplay, wipe_perdisplay): New functions.
(init_keyboard): Move perdisplay initialization to init_perdisplay.
(syms_of_keyboard): Likewise.
(echo_prompt, echo_char, echo_dash, echo, cancel_echoing, echo_length)
(read_char, Fdiscard_input, stuff_buffered_input): Use current_perdisplay,
not get_perdisplay.