uts: gfx_private implement cls callback & visual_io v4
uts: gfx_private add alpha blending
uts: provide fb_info via fbgattr dev_specific array.
uts: identify FB types and set up gfx_private based on type.
uts: gfx_private should use setmode drm callback.

apply https://www.illumos.org/rb/r/1356/ and boot. Note that alpha blend needs update in tem to make text to appear on screen with 32-bit depth.