egl: fix some #ifdef guards
egl: fix some #ifdef guards

In the winsys vtable .xlib_get_visual_info and
.onscreen_x11_get_window_xid should be guarded by the
COGL_HAS_EGL_PLATFORM_POWERVR_X11_SUPPORT because they need to be there
if cogl is configured with --enable-xlib-egl-platform but not if just
configured with --enable-xlib.

Distrotech/cogl,djdeath/cogl-android,Distrotech/cogl,djdeath/cogl-android,gcampax/cogl,djdeath/cogl,collects/cogl,spatulasnout/cogl,gcampax/cogl,spatulasnout/cogl,djdeath/cogl,djdeath/cogl,gcampax/cogl,Distrotech/cogl,djdeath/cogl-android,gcampax/cogl,collects/cogl,Distrotech/cogl