Move bget to libutils replacing dlmalloc

* Moves bget to libutils replacing dlmalloc as kernel memory allocator
* Restores the code formatting of bget.{c,h} to the original state as
  parts of the current code was unreadable
* Adds malloc_add_pool() to make use of previously unused memory
* Moves call to malloc_init() into platform specific code
* Restores MDBG into working condition
* Adds memalign function to bget.

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Tested-by: Jens Wiklander <jens.wiklander@linaro.org> (QEMU virt platform)
Perhaps these should be renamed `__heap_start` and `__heap_end` for consistency with plat-vexpress and with other symbols in `plat-stm/tz-template.lds` (`__bss_end`, `__stacks_start`...)?