libsdl2: require GLES when building Wayland support
The Wayland support requires GLES2 to be enabled as otherwise the EGL support
code in SDL2 isn't enabled.
| In file included from .../SDL2-2.0.3/src/video/wayland/SDL_waylandvideo.c:34:0:
| .../SDL2-2.0.3/src/video/wayland/SDL_waylandvideo.c: In function 'Wayland_CreateDevice':
| .../SDL2-2.0.3/src/video/wayland/SDL_waylandopengles.h:38:38: error: 'SDL_EGL_GetSwapInterval' undeclared (first use in this function)
| #define Wayland_GLES_GetSwapInterval SDL_EGL_GetSwapInterval
Solve this by adding gles2 to the Wayland PACKAGECONFIG option.
Signed-off-by: Ross Burton <ross.burton@intel.com>
