surfaceflinger: add RenderEngine::setCurrentSurface

setCurrentSurface is a wrapper to eglMakeCurrent and it uses the EGL
context implied by the RenderEngine.  This also allows us to
simplify DisplayDevice::makeCurrent.

Test: SurfaceFlinger_test
Change-Id: Idab581f0ef79af7263159a558d8fad493a198ce7
5 files changed