Provide AGL extension, wl_shell support for Weston ivi-shell.

Provide AGL extension, wl_shell support for Weston ivi-shell.

This component is merged in meta-agl/meta-ivi-common. Additionally,
AGL demo, Home screen, requires, wl_shell support as well. This patch
just makes two function extern to be used by Wayland-IVI-Extension to
support wl_shell. This means this patch doesn't change bihavior of
ivi-shell but allows Wayland-IVI-Extension to get notification of
creation of wl_shell and send configure to the application.

In details, please visit AGL wiki and Wayland-IVI-Extension's README

https://wiki.automotivelinux.org/agl-distro/demo-apps/home-screen

Change-Id: If300ca9ecc62a78e473e01ef670cd9a366fe44e0
Signed-off-by: Nobuhiko Tanibata <ntanibata@jp.adit-jv.com>