mm: enumerate all gfp flags

mm: enumerate all gfp flags

Introduce GFP bits enumeration to let compiler track the number of used
bits (which depends on the config options) instead of hardcoding them.
That simplifies __GFP_BITS_SHIFT calculation.

Link: https://lkml.kernel.org/r/[email protected]
Suggested-by: Petr Tesařík <[email protected]>
Signed-off-by: Suren Baghdasaryan <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Pasha Tatashin <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: Petr Tesarik <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>