Improve the build system, making it more flexible

[vacantron]

Given the growing scale of the project, the Makefile becomes more complex to set various kinds of features and check the related prerequisites. Using the automatic build tool might help us simplify these works.

[jserv]

I plan to take an incremental approach, starting by enhancing the existing modular GNU Make-based build system before eventually transitioning to other build systems once the current issues are resolved. The first step will be to introduce Kconfiglib, as done in the Mado project, to streamline option dependency tracking and reduce code bloat in the Makefile. Additionally, Mado's updated mk/common.mk provides a collection of helper rules for GNU Make that simplify managing source and target files. These rules efficiently handle multiple targets, dependencies, and useful file generation throughout the build process. Adopting this refined script could make the rv32emu build system more flexible and maintainable.