drm/amdgpu/gfx: Clear more EDC cnt

Clear SDMA and HDP EDC counter in GPR workarounds.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>