Set sane defaults fori the reference clock for Rage XL and Mobility cards

on sparc64.  This makes it possible to run X without an xorg.conf on machines
like the blade100 and the Tadpole laptops.

ok oga@, matthieu@

driver/xf86-video-mach64/src/aticonfig.c

@@ -358,6 +358,10 @@ ATIProcessOptions
     Accel = CacheMMIO = HWCursor = TRUE;
 
     ReferenceClock = ((double)157500000.0) / ((double)11.0);
+#ifdef __sparc__
+    if (pATI->Chip == ATI_CHIP_264XL || pATI->Chip == ATI_CHIP_MOBILITY)
+	    ReferenceClock = 29500000.0;
+#endif
 
     ShadowFB = TRUE;