Introduce new APIs in essp_heap_caps.h:
- heap_caps_walk()
- heap_caps_walk_all()
Those functions are triggering a callback for all blocks
(allocated or free) of memory present in heaps meeting
the set of capabilities passed as parameter (or all heaps
for heap_caps_walk_all() function)
test_walker.c added to test the new functionality in
test_apps/heap_test/