Rename build option WITH_WAYLAND by WITH_GHOST_WAYLAND.

Build options to select backends for Ghost system use the convention
WITH_GHOST_<Backend name>.

We rename the Ghost build option WITH_WAYLAND by WITH_GHOST_WAYLAND to
obey this convention.
Separate EGL from Wayland.

EGL build has its own build option called WITH_EGL, so it makes easier
if we want to use EGL for non Wayland builds later on.