gstreamer1.0-plugins-bad: add packageconfig for egl

gstreamer1.0-plugins-bad: add packageconfig for egl

In commit 9c3a94aea1d (gstreamer1.0-plugins-bad: Move EGL requirement for
Wayland), --enable-egl was explicitely added to the wayland packageconfig. While
this is correct that enabling wayland requires egl, it should be possible to
enable egl without wayland, even when using X11. For example, glimagesink can be
used for GPU based color conversion using EGL/GLES.

As such, let's make egl and wayland two separate PACKAGECONFIG flags.

Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>