viafb: improve viafb_par

This patch introduces viafb_shared and is the beginning of a smooth
transition to use it.

viafb_shared should contain all general, non-surface specific data that
should be shared along all viafb framebuffers while viafb_par should only
contain things that are specific to each surface or in other words extend
fb_info.  This change is intended to clean the dual/multi framebuffer
handling up.

This removes the annoyance that viafbinfo1->par points to a different
structure than viaparinfo1.

As the last change is fundamental it is difficult to ensure that all parts
of the driver do not depend on the previous brokenness but the chance of
regressions is very low.

Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Scott Fang <ScottFang@viatech.com.cn>
Cc: Joseph Chan <JosephChan@via.com.tw>
Cc: Harald Welte <laforge@gnumonks.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>