Revert "drm/amdgpu/sdma_v4_4_2: update VM flush implementation for SDMA"

this temporarily  reverts commit 'commit 47cad920 ("drm/amdgpu/sdma_v4_4_2: update VM flush implementation for SDMA")'
it cause a regression.

Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>