infra: Change BR2_HOST_NEEDS_JAVA name

Change BR2_HOST_NEEDS_JAVA to BR2_NEEDS_HOST_JAVA as it makes more
sense.
The host doesn't need Java but Buildroot needs the host to have
Java in order to build the package that select this option.

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>