Read back harvest configuration from registers and simplify
calculations.  No need to program the raster config registers.
These are programmed as golden registers and the user mode
drivers program them as well.

v2: rebase on Tom's patches
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>