egl: Allow 24-bit visuals for 32-bit RGBA8888 configs

egl: Allow 24-bit visuals for 32-bit RGBA8888 configs

Previously only the 32-bit X visual would match the 32-bit RGBA8888
configs.  This resulted in every config with alpha getting the "magic"
visual whose alpha is used by the compositor.  This also resulted in no
multisample visuals being advertised.  How many ways could we lose?

This patch inverts the problem... now you can't get the visual with
alpha used by the compositor even if you want it.  I think we need to
invent a new value for EGL_TRANSPARENT_TYPE that apps can use to get
this.  I'm surprised that there isn't already a choice for
EGL_TRANSPARENT_ALPHA.

NOTE: This is a candidate for the 9.1 branch.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Tested-by: Tian Ye <yex.tian@intel.com>
Acked-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=59783