Revert the changes in c5dd5fef0690cce11ba9d65220c7bf2a0617ee11

[Removed 24 bit visual - we use 32 bit visuals for RGB888.]

With 32 bit visuals, xfwm and glmarks-es2 fullscreen were displaying correctly.
But there were issues the decorations on windowed egl apps, and some egl fullscreen apps like XBMC after exiting will leave the screen black (although nothing would crash).
This goes back to creating 2 visuals, for 24 bit and 32 bit.