weston_6.0.0.bb has multiple egl & mesa DEPENDS

Our ported weston 6 recipe (meta-agl-bsp/recipes-graphics/wayland/weston_6.0.0.bb)

does use virtual/mesa in

but also virtual/egl

This works if both are set to mesa, bug fails in case virtual/egl is set differently and then

we can see conflicts:

Upstream solved this in later versions of the recipe by not relying on virtual/mesa but the virtual/egl virtual/libgles2 directly.

Thus apply this solution to our recipe as well.