viafb: hardware acceleration initialization cleanup

The main motivation of this patch was to merge the three initialization
functions in one and clean it up. However as some changes in other code
areas where needed to do it right some small other changes were made.

Changes to viafb_par:

io_virt renamed as engine_mmio and moved to shared
VQ_start renamed as vq_vram_addr and moved to shared
VQ_end removed as it is easily recalculatable

vq_vram_addr is not strictly needed but keep it to track where we
allocated video memory.  The memory allocated for the virtual queue was
shrunk to VQ_SIZE as VQ_SIZE+CURSOR_SIZE looked like a bug to me.  But to
be honest I don't have the faintest idea what virtual queues are for in
the graphic hardware and whether the driver needs them in any way.  I only
know that they aren't directly accessed by the driver and so the only
potential current use would be as hardware internal buffers.  For now keep
them to avoid regressions and only remove the double cursor allocation.

The most changes were caused by renames and the mentioned structure
changes so the chance of regressions is pretty low.  The meaning of
viafb_accel changed slightly as previously it was changed back and forth
in the code and allowed to enable the hardware acceleration by software if
previously disabled.  The new behaviour is that viafb_accel=0 always
prevents hardware acceleration.  With viafb_accel!=0 the acceleration can
be freely choosen by set_var.  This means viafb_accel is a diagnostic tool
and if someone has to use viafb_accel=0 the driver needs to be fixed.

As this is mostly a code cleanup no regressions beside the slightly change
of viafb_accel is expected.

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>