add geist's libc without malloc/heap_alloc

Add related string functions, printf, and debugging support from lk's
libc library. The functions that make use of malloc/heap_alloc were
removed as we do not currently have memory management. These memory
operations will be added later.

The available functions are self-documented in include/{debug.h,
stdio.h}, lib/libc/, and lib/libc/string/ directory.
lib/debug: remove debug_print function

Remove debug_print which was added to test new build system. Now that we
have related libc functions for debugging and printing, we do not need
it.