malloc: Cleanup macros, asserts and sysmalloc_mmap_fallback.

[Wilco Dijkstra]

Hi William,

> Refactor malloc.c to remove dead code, create macros to abstract duplicated 
> code, and cleanup sysmalloc_mmap_fallback to remove logic not related to the 
> mmap call.

LGTM. Thanks for the cleanup.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

I've committed it for you.

Cheers,
Wilco