[PATCH 1/9] drm/radeon/kms: improve evergreen 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 dimensions
make 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.