build: change FREE_KERNELS option to ENABLE_NONFREE_KERNELS

It was noted that FREE_KERNELS may be confusing since with =OFF it
actually enables non-free kernels (wihtout published sources). So,
let's use ENABLE_NONFREE_KERNELS instead.

Mind that ENABLE_NONFREE_KERNELS default value is ON. So, driver
default behaviour did not change.

v2: further typo corrections in README.md

Change-Id: Ifae417c3ada32d065fa615c9d5cc17c41f3b93b5
Signed-off-by: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
13 files changed