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/20240224015800.2569851-1-surenb@google.com


Suggested-by: Petr Tesařík <petr@tesarici.cz>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Petr Tesarik <petr@tesarici.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>