msm: mdss: remove interrupt handler when pingpong is not present

Remove pingpong interrupt handler when pingpong done interrupt is
not present. This will ensure no unexpected pingpong is reported
which might lead to confliction with the destroying ctx.

Change-Id: I9a7173fb19e55344cedcfeccdaf23efaba11892c
Signed-off-by: Ray Zhang <rayz@codeaurora.org>