glx: Store the RENDER_TYPE in indirect rendering

glx: Store the RENDER_TYPE in indirect rendering

v2 (idr): Open-code the check for GLX_RENDER_TYPE.
dri2_convert_glx_attribs can't be called from here because that function
only exists in direct-rendering builds.  Also add a stub version of
indirect_create_context_attribs to tests/fake_glx_screen.cpp to prevent
'make check' regressions.

Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>