Revert "Revert "drm/amdkfd: Add heavy-weight TLB flush after unmapping""

This reverts commit 430f8e6e.

Revert reason: Issue has been resolved.

Signed-off-by: Eric Huang <jinhuieric.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>