mdss: mdp3: Validate input from userspace

Fully verify that the values from client are safe to use.

bug: 28602014

Original-Change-Id: I73d6839f5bccd53b8bc2d812dc7673b13735299c
Change-Id: I8aa16d9a361a668a394b0ef8644f1d00d92c4f1b
Signed-off-by: Terence Hampson <thampson@codeaurora.org>