mdss: ppp: add sync point to ppp, allowing for async ppp blit

It is a requirement that PPP be async and should use sync points
and fences to wait for buffers and communicate that it is done
using release fence

Change-Id: I35663737dd4bd4a52bb12b2a31ed06f3d5a69f31
Signed-off-by: Terence Hampson <thampson@codeaurora.org>