msm: mdss: validate layer count before copying userdata

Validate input layer count in rotator and async update
ioctl call before copying the rotator request list and
async update layer list.

Change-Id: I3489e5a2d4237a47bddf56c2f44c9e3001f0b2b4
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>