unicode: cache the normalization tables in struct unicode_map

Instead of repeatedly looking up the version add pointers to the
NFD and NFD+CF tables to struct unicode_map, and pass a
unicode_map plus index to the functions using the normalization
tables.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>