Video glitches, mostly sprites

[Spritetm]

Need to figure out:

• Sprites: when enabled (and possibly scaled), they mess up the first column of the LCD. Possibly related: when scaling sprites, there's sometimes extra crap drawn on the left side.
• Gfx subsystem in general: sometimes the screen is drawn a bit lower for one frame. Possibly some interaction between the frame buffer DMA reader and the rest of the gfx hardware? If any, if DMA doesn't return framebuffer bytes, the GFX hardware stalls. (Unless the FB layer is disabled... hmmm, can test that.)