Revert "linux: only depend on host-lzop if needed"

This reverts commit ca80782f. 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>