[wam][cef] Add the CEF recipe

This change makes it possible to build applications that depend on
libcef, and also adds a few changes picked from our previous
implementation that enables the applications to communicate with the
agl-compositor.

Bug-AGL: SPEC-3872

Signed-off-by: Roger Zanoni <rzanoni@igalia.com>
Change-Id: I215138b8f5d63da84ada2f8c006f4025f0b3fafb