drm/radeon: don't reset dma on NI/SI init

Otherwise we may lose the DMA golden settings which can
lead to hangs, etc.

bug:
https://www.libreoffice.org/bugzilla/show_bug.cgi?id=83500



Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org