i2c: npcm7xx: Annotate register field definitions with longer names

To make the code easier to understand, add longer names to the
definitions of register fields. These longer names are based on source
code published by DELL/AESS for WPCM450, but should apply just as well
to NPCM7xx and NPCM8xx.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Tali Perry <tali.perry1@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>