The Driver is specific to a processor but not to a board. The Kernel is specific to a board (and therefore a processor). For example the module d4001.c is a driver for the 4001 processor. It contains information about what registers are present on the processor. Whereas the module k4001.s is a kernel for the BDMR400x evaluation board, and because of the similarities it is possible to use this kernel on a BDMR400x fitted with a 4001, 4002, or 4003 (although you might need to provide software multiple/divide emulation if your board is equipped with a 4002, or 4003).
By default, the makefile will list all of the possible targets for this directory. You can type "make all" to build everything, or if you wish to build just those files appropriate for a specific target type (eg. 4102), you can type "make 4102", or even "make k4102" if all you need is the kernel.