msm: mdss: free splash memory for MSM8909w after splash done

Splash memory free calls was failing for MSM8909w because
splash memory length was not populated properly after device tree parsing.
Use cont-splash-memory property to read splash mem length when
memblock-reserve is not defined.

Change-Id: I1a79c1a6eeb2da6f8238bcc1f82ccad0c6891569
Signed-off-by: Sachin Bhayare <sachin.bhayare@codeaurora.org>