i965: Disable ARB_fragment_shader_interlock for platforms prior to GEN9

ARB_fragment_shader_interlock depends on memory fences to
ensure fragment ordering and this ordering guarantee is
only supported from GEN9 onwards.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109980
Fixes: 939312702e "i965: Add ARB_fragment_shader_interlock support."
Signed-off-by: Plamena Manolova <plamena.n.manolova@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/compiler/brw_fs_generator.cpp

@@ -2100,6 +2100,7 @@ fs_generator::generate_code(const cfg_t *cfg, int dispatch_width)
          break;
 
       case SHADER_OPCODE_INTERLOCK:
+         assert(devinfo->gen >= 9);
          /* The interlock is basically a memory fence issued via sendc */
          brw_memory_fence(p, dst, BRW_OPCODE_SENDC);
          break;