Previous kernel version provided the current CPU inside of task_struct
directly.
This is not the case anymore, and the current CPU has to be extracted by
using information from thread_info, which is only provided if
CONFIG_THREAD_INFO_IN_TASK is enabled in the kernel config.

Builds without CONFIG_THREAD_INFO_IN_TASK will be aborted.

Note: I am not confident that this is the complete and correct solution,
however the most practical one. (I.e. feel free to overrule it down the
road)

The previously used functions get_online_cpus() and put_online_cpus()
have been removed in 8c854303ce0e38e5bbedd725ff39da7e235865d8.
As both functions where pure aliases they are replaced with the calls
they were previously pointing to, cpus_read_lock() and cpus_read_unlock().

The driver module depends on the definition module.
dkms offer the variable BUILD_DEPENDS for that, even if it notes that it
is not necessarily enforced this should be used to avoid build failures.

In Linux kernel commit 39808e451fdf ("kbuild: do not read
$(KBUILD_EXTMOD)/Module.symvers") the in x86_adapt used way of communicating
dependencies for symbols of other modules has been updated.

This commit applies this new method to the x86_adapt_driver module by
setting the variable KBUILD_EXTRA_SYMBOLS in the make file.

The previous version used shell globbing to find files, which also
returned directories which failed in the subsequent call to sed.

The fix is to search for files only using `find DIR -type f` and apply
sed only to these found files.