Increment/decrement a counter around EGL calls

This is in preparation for a change that will hibernate the underlying
EGL when idle. Instead of a bare egl_display_t*, get_display() now
returns a egl_display_ptr, which acts like a smart pointer. The
"wakecount" counter managed by the smart pointer isn't used for
anything in this change. It will be used to make sure we don't
hibernate when any thread is in an EGL call, without having to hold a
mutex for the duration of the call.

Change-Id: Iee52f3549a51162efc3800e1195d3f76bba2f2ce