package/libegl: add option for wayland extensions

package/libegl: add option for wayland extensions

Wayland requires that an OpenGL/EGL implementation provides a few
extensions, so that wayland servers and clients can exchange buffers.

Currently, only one OpenGL/EGL implementation provides those extensions:
mesa3d.

However, other implementations are catching up, especially the
proprietary NVidia driver, which has as of late introduced those
extensions. Other, non-public implementations may also provide those
extensions.

A lot of wayland-related packages require those extensions, and
currently they have to depend on mesa3d to provide OpenGL/EGL, which
precludes using those packages when a non-mesa3d provider is enabled,
even when that providers implements the necessary extensions.

Add an option to the libegl virtual package, that providers on
OpenGL/EGL can select to state they provide those extensions.

Packages that need those extensions can additionally depend on this new
option, instead of the existing libegl package.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>