x86: unify gfp masks

Use the same gfp masks for x86_64 and i386.
It involves using HIGHMEM or DMA32 where necessary, for the sake
of code compatibility, (no real effect), and using the NORETRY
mask for i386.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>