kernel - Correct unaligned results in alist_free_info()

kernel - Correct unaligned results in alist_free_info()

* alist_free_info() needs to return a power-of-2-sized and power-of-2
  aligned result in order for the caller to be able to use the information
  to allocate the resulting space.

* Fixes an issue where the kernel is unable to return a big chunk of the
  reserved DMA space back to the kernel free pool, resulting in a lot of
  wasted memory.