[PATCH] zd1211rw: Generic HMAC initialization

Many of the registers written during ZD1211 HMAC initialization are
duplicated exactly for ZD1211B. Move the identical ones into a generic
part, and write the hardware-specific ones separately.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>