lib: Provide MAX and MIN in system.h

lib: Provide MAX and MIN in system.h

This change also creates a new header file libeu.h to provide the
prototypes for the function of libeu. That hides the definition of function
crc32, which can conflict with zlib, from libelf. It also prevents mistakes
to refer those functions from a component which doesn't link with libeu,
such as libelf.

Signed-off-by: Akihiko Odaki <akihiko.odaki.4i@stu.hosei.ac.jp>