disp: msm: sde: allow fence signalling during crtc disable

With the new ASYNC power-mode changes, user-mode can
request for retire/release fences during power-mode
changes. This is used as a signal for power-mode
completion by user-mode. Allow preparing/signalling
these fences during crtc enable/disable to support it.

Change-Id: I7709cd4762c8d77776ba6ba2d07aa6b76b5262d0
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>