Long story short, this fixes sporadic hardlocks with my rv410 during
times of intense 2D acceleration (Flash on Fx3).
V2: Fix indentation and move errata_fini to suspend function so we
don't leak scratch register over suspend/resume cycle.
V3: Move scratch_reg to asic specific structure (aim is to slowly
move stuff to asic specific structure and avoid poluting
radeon_device struct with asic specific variables)