Enable TearFree if it's set to auto and VariableRefresh is enabled

As of kernel commit 1ca67aba8d11 ("drm/amd/display: only accept async flips for fast updates"), we reject async flips that used to be silently degraded to vsync. However, this causes issues for VRR if TearFree isn't enabled, in particular we have seen that VRR fails to engage on a handful of tested applications and in one case we even observed an application soft hang. So, if TearFree is set to auto we should enable it if VariableRefresh is enabled and we should warn users if they try to enable VariableRefresh while TearFree is disabled.

Signed-off-by: Hamza Mahfooz hamza.mahfooz@amd.com