changed behaviour of malloc(0) and optimized calloc

[ZERICO2005]

__simple_malloc and __standard_malloc now return NULL when malloc(0) is called.

calloc (when __TICE__ is defined) now uses an inlined implementation of bzero which uses the $E40000 address to speed up the zero filling of memory.

Otherwise, it will use the previous memset implementation when __TICE__ is undefined.

[ZERICO2005]

To reduce the complexity of this PR, I undid the allocator switches to nonzero_fill_calloc when malloc(0) is known to return NULL commits for now (which essentially added 4 different calloc variants). That way we can focus on the two important changes that will be made in this PR:

• Changing the behavior of __simple_malloc(0) and __standard_malloc(0) to return NULL.
• Optimizing calloc zero filling by using the $E40000 all zeros address

[runer112]

If all checks pass, seems good.