msm: mdss: make timing db property DSI controller specific

If timing db(Double Buffered) property is enabled, then MDP FLUSH
bit needs to be set in order to push the data to video interface.
Currently this property is used as a shared property for both DSI
interfaces. But in case of chipsets where there is no FLUSH bit
defined for the secondary DSI interface, this will cause issue.
So moving the property to each controller specific instead of shared.

Change-Id: I25913867da41ca2fb2848ab96f5be5d9228a8f63
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>