Setting a mode seems to clear the cursor registers, so we need to
re-program them to make sure the cursor is visible.

Port of radeon commit:
6d3759fa

v2: change radeon reference in error message
Reviewed-by: NMichel Dänzer <michel.daenzer@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>