Make objects collection a member of egl_display object

Move EGL objects (contexts, surfaces, ...) collection from global
static into EGL display object. Since EGL implementation currently
supports only one display, this doesn't change current logic. This
aims at preparing for next coming changes in eglTerminate() to
support per-display cleanup.

Bug: 4152714
Change-Id: I5e424781b89c3c275f9922f943463d5f6b1f6bc6