kmsplayerendpoint: Synchronize elements after linking them

Change-Id: I43572155b2cfbe2f534844c7610c92708237d2a9
kmsplayerendpoint: Force caps negotiation in appsrc using the fixed caps set in appsink through event caps

Change-Id: I1e1dad7ed2fdbdf4e36173377dcc6611ca9f9527