erts: Remove faked MSEG_ALLOC

* Not used except in valgrind but there mseg is disabled completely
  via Meamin.
erts: Let mseg allocate larger alignments
erts: Teach mseg alloc the value of halfword beam
erts: New mseg allocator cache

* utilize the power of two
erts: Fix compiler warnings for halfword vm
erts: Add carrier offset to internal allocation headers
erts: Move carrier alignment define to erl_msg.h
erts: Use new mseg flag argument for carrier sizing
erts: Make alloc_SUITE:bucket_mask handle larger carriers
erts: Change single carrier block header flags

to allow realloc to determine block size (in MBC or SBC)
without having to read the footer of the previous block
that might be written to by concurrent thread.
erts: Refactor erl_alloc_util.c

Make use of type FreeBlkFtr_t
Rename GET_MB_CARRIER into BLK2MBC (like BLK2SBC)
Remove some unused macros
erts: Save one word per block for thread preferred allocators

by making use of the new block header scheme to find the carrier header
and thereby the allocator.
erts: Refactor removing dummy footer in carrier header
erts: Refactor renaming a couple of macros in alloc_util

To get a consistent naming scheme where
FBLK = Free block
ABLK = Allocated block
erts: Add carrier pointer to header of free block
erts: Ensure MBC limits due to super alignment
erts: Fix alloc_SUITE:coalesce for new header scheme
erts: Enable new header scheme without super alignment on 64-bit
erts: Fix compile warnings in alloc_util
erts: Cleanup minor things in alloc_util