infra: remove redundant $(call) on pkgdir, pkgname, pkgparentdir

When calling make 'functions', the $(call) keyword is only needed if the
function takes arguments. For pkgdir, pkgname and pkgparentdir this is not
the case, so we can remove the call to make things more readable.

Suggested-by: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>