Refine granularity handling in preparation of AT45DB series support.

This adds a number of new granularitie and refines the handling of
n-byte granularities by extracting the respective code into a helper
function which reduces the pain of the above significantly.

Signed-off-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>
Acked-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>

git-svn-id: svn://flashrom.org/flashrom/trunk@1666 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1