bn/asm/armv4-gf2m.pl, modes/asm/ghash-armv4.pl: faster multiplication

algorithm suggested in following paper:

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
(cherry picked from commit f8cee9d0)