package/nodejs: add BR2_PACKAGE_HAS_NODEJS
Commit ccf3536fcbfb2f3744ef7ccf1ed1b75d6d1f22ac ("package/nodejs: make
target nodejs package virtual") forgot to introduce the
BR2_PACKAGE_HAS_<foo> boolean option matching the newly introduced
virtual package, causing check package warnings.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>