kconfig: speed up all*config + randconfig

Drop the chatty mode when we generate the all*config, randconfig
configurations.
Ths speeds up the process considerably and noone looked
at the output anyway.
This patch uses the conf_set_all_new_symbols() function
just added to kconfig.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Roman Zippel <zippel@linux-m68k.org>