core: fix arithmetic on a pointer to void

Use char* instead of void* for this
pointer arithmetic. Fixes the following:

error: arithmetic on a pointer to void
buf = buf + offset;
      ~~~ ^

Change-Id: I6cfc92c9240fda66a52e780cda7820fdba76914a
EGL14.eglCreateWindowSurface should set producerControlledByApp

Interface of Surface class changed.
To reflect the change for EGL14, add producerControlledByApp flag.
Similar change can be seen in 0fa257fe53bf520bdde93996a1901ce6bc3e1788

Change-Id: Ic8911d3131e033747cfdabe59ac2fea1e90bb4a0