egl: Add funtions to link contexts and surfaces to displays.

egl: Add funtions to link contexts and surfaces to displays.

EGL contexts and surfaces are resources of displays.  They should be
managed by displays.  This commit adds a bunch of functions to
egldisplay.c to help establish the links between contexts/surfaces and
displays.  How links are established is considered opaque outside
display.  Functions like _eglGetSurfaceHandle or _eglLookupSurface are
therefore moved to egldisplay.c, with some small modifications.

The idea is also extended to display.  That is, displays need to link to
themselves to be looked up.

This commit only adds the functions.  A commit to use them should
follow.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>