Revert "linux: fix the KCONFIG_GET_OPT calls to be inside a BR2_LINUX_KERNEL test"

This reverts commit 4ad1ea59. 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>