viafb: split global index up

viafb: split global index up

This is the first step to remove an artificial global index that was used
in two ways:

1. As a pseudo index in the mode table.  Pseudo as you had to search
   through the table to find the referenced entry.  This was replaced by
   using a pointer to the entry.

2. As a shortcut to compare a combination of horizontal and vertical
   resolution at the same time.

   This was replaced by a "(hres<<16) | vres" which is good enough for
   now and the near future.  If vres or hres become greater than 2^16 this
   might indeed cause problems but this solution allows to split this
   indexing mess up without the requirement to do even more code changes.

This is a big change that will allow more clean ups.  It should be a bit
faster but that is probably not relevant for normal operation.  No
regressions expected but as this is a relatively big step heavy testing is
appreciated.

Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Joseph Chan <JosephChan@via.com.tw>
Cc: Scott Fang <ScottFang@viatech.com.cn>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>