Revert "packages infra: add function to get a Kconfig option"

This reverts commit c28a28ee. The
whole host-lzop optional dependency logic cannot work, since the
configuration file will only be known after the kernel sources are
extracted, if an internal kernel defconfig is used, which is quite
common.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>