configure: cleanup classic dri drivers handling
configure: cleanup classic dri drivers handling

* Make sure that only drivers that are handled by configure.ac
are included in DRI_DIRS.
* Change with_dri_drivers default value to auto, and set enable
autodetection, when enable_opengl is on.

v2: Move "test" to the correct location.
v3: Squash DRI_DIRS handling before the switch statement.
Suggested by Ilia Mirkin

Signed-off-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>
Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

zz85/glsl-optimizer,dellis1972/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,zeux/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,zz85/glsl-optimizer,zz85/glsl-optimizer,zz85/glsl-optimizer,tokyovigilante/glsl-optimizer,djreep81/glsl-optimizer,jbarczak/glsl-optimizer,djreep81/glsl-optimizer,dellis1972/glsl-optimizer,tokyovigilante/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,mapbox/glsl-optimizer,benaadams/glsl-optimizer,mcanthony/glsl-optimizer,jbarczak/glsl-optimizer,benaadams/glsl-optimizer,bkaradzic/glsl-optimizer,mapbox/glsl-optimizer,bkaradzic/glsl-optimizer,metora/MesaGLSLCompiler,dellis1972/glsl-optimizer,mapbox/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,wolf96/glsl-optimizer,zz85/glsl-optimizer,jbarczak/glsl-optimizer,jbarczak/glsl-optimizer,djreep81/glsl-optimizer,djreep81/glsl-optimizer,zeux/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,metora/MesaGLSLCompiler,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,zz85/glsl-optimizer,wolf96/glsl-optimizer,metora/MesaGLSLCompiler,benaadams/glsl-optimizer,zeux/glsl-optimizer,wolf96/glsl-optimizer,mapbox/glsl-optimizer,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer