Use const for some arrays and functions.

Use const for some arrays and functions.
* src/xterm.h (xg_set_icon_from_xpm_data):
* src/xfns.c (xg_set_icon_from_xpm_data):
* src/term.c (fkeys):
* src/keyboard.c (lispy_accent_keys, lispy_function_keys)
(lispy_multimedia_keys, lispy_kana_keys, iso_lispy_function_keys)
(lispy_drag_n_drop_names, scroll_bar_parts, modify_event_symbol)
(frame.c frame_parms):
* src/emacs-icon.h (gnu_xpm_bits):
* src/callint.c (callint_argfuns): Use const.