drm: uapi: add destination scaler interface

Added interface for the user space to provide the number of
destination scalers to be configured along with the configuration.
Configuration includes flags, new mixer width and height,
destination scaler block index and parameters.

Change-Id: I6e80b4fcaad99d6f4e75885a1cf556ba88b3a632
Signed-off-by: Sravanthi Kollukuduru <skolluku@codeaurora.org>