drirc: Allow extension midshader for Metro Redux

This fixes both Metro 2033 Redux and Metro Last Light Redux

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99730


Signed-off-by: Eero Tamminen <eero.t.tamminen@intel.com>
Signed-off-by: Vadym Shovkoplias <vadym.shovkoplias@globallogic.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
(cherry picked from commit e0de26ea)