This change removes the kernel release from the full kernel version.
This is used by Proxmox to identify differences in the kernel ABI.
However, since this project does not track these changes, we remove the
kernel release number altogether.
This change updates the build code to support in-tree builds. This is
easier to manage for CI builds and reduces the amount of IO operations
necessary for the build process.
the top-level Makefile now only prepares the build directory by copying
and patching sources and generating the real files from debian/*.in
the actual build and packaging happens in debian/rules
