cmake: disable building of ccmake

To speedup building disable ccmake because it's not needed by buildroot.
Also disabling ccmake get rid of the ncurses optional unspecified
dependency for the sake of reproducible builds.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Jerzy Grzegorek <jerzy.grzegorek@trzebnica.net>
Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Cc: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Samuel Martin <s.martin49@gmail.com>
Cc: Alexander Potashev <aspotashev@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>