GCM was broken in non-AESNI mode because I fluffed a #define when
moving gcm128.c across.

Change-Id: I66d5fed6a3d83d641da55c5ca434f17db0d89237

Câmara, D.; Gouvêa, C. P. L.; López, J. & Dahab, R.: Fast Software
Polynomial Multiplication on ARM Processors using the NEON Engine.

http://conradoplg.cryptoland.net/files/2010/12/mocrysen13.pdf

(Imported from upstream's 0fb3d5b4fd)

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)