FFL-2501: retain only one Linux kernel packageThis is the upstream way of kernel building. The advantage is that upgradingto newer Buildroot versions is much easier than before. Also, writing newpackages that build and install Linux kernel modules is easier. Finally, due toFBR_ADDITIONAL_KERNELS, it is possible to build other Linux kernel versions fortesting.Now, the linux-kernel-modules package is obsolete and has been removed. Use"fbr-make linux-modules" instead in order to build all Linux kernel modules.pkg-generic.mk has been extended such it is now possible to group all Linuxkernel patches per major version number and not per complete version number.