[PATCH 2/9] drm/radeon/kms: improve r6xx blit code

[Ilija Hadzic]

start with first-cut conceptual patch from Alex Deucher
(commit info below); turn on 1D tiling
make rectangular buffer always 2:1 or 1:2 ratio
make buffer dimenstions an integer multiple of unit
dimensionsmake sures that integral number of pages map
to the buffer fix a few bugs that resulted in incorrect
dimensions tidy up a little bit to get rid of an ugly
if/else parametrize some "magic" constants
add protections from illegal buffer sizes etc.