msm: mdss: rename qcom,has-dst-split property to qcom,has-pingpong-split

Rename qcom,has-dst-split device tree property with qcom,has-pingpong-split
to align terminology used by the hardware and software drivers.

Change-Id: I8af3809f6c28d232dee457901719b6f13a216c76
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>
Signed-off-by: Shivaraj Shetty <shivaraj@codeaurora.org>