[arch][mmu] align the return of arch_mmu_map and arch_mmu_unmap of all the arches

[travisg]

No description provided.

[travisg]

Currently most of the arches return simply an error condition or not if the map/unmap went through, and try to clean up if there's a partial map. The arm32 code returns the number of pages mapped, which is why the return code is an int. Move the arm32 code to the former, probably.