pkg-cmake.mk: replace "echo -en" with printf

printf is POSIX-compliant, echo -e is not.

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>