kconfig: remove useless 'default n'

kconfig bools are disabled by default, so specifying 'default n' is useless and
noisy. This patch removes all occurrences of 'default n'.

Signed-off-by: "Benoît THÉBAUDEAU" <benoit.thebaudeau@advansee.com>

 reporter_name="Remy Bohmer"

 reporter_url="linux@bohmer.net"

 reporter_comment="Example for building a toolchain for m68000 bare metal targets"