mm: add comments for allocation helpers explaining why they are macros

mm: add comments for allocation helpers explaining why they are macros

A number of allocation helper functions were converted into macros to
account them at the call sites.  Add a comment for each converted
allocation helper explaining why it has to be a macro and why we typecast
the return value wherever required.  The patch also moves
acpi_os_acquire_object() closer to other allocation helpers to group them
together under the same comment.  The patch has no functional changes.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 2c321f3f70bc ("mm: change inlined allocation helpers to account at the call site")
Signed-off-by: Suren Baghdasaryan <[email protected]>
Suggested-by: Andrew Morton <[email protected]>
Cc: Christian König <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: Thorsten Blum <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>