kbuild: use KECHO convenience echo

Convert a few echos in the build system to new $(kecho) so we get correct
output according to build verbosity.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
[sam: added kecho in a few more places for O=... builds]
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>