Renamings for OBMC experiment

To get ready for pulling AV1 to nextgenv2
Replace the experimental flag by MOTION_VAR. Rename major variables.

Change-Id: If6cf4f37b9319c46d8f90df551cc7295d66ca205

av1/encoder/mcomp.c

@@ -2930,7 +2930,7 @@ int av1_masked_full_pixel_diamond(const AV1_COMP *cpi, MACROBLOCK *x,
 }
 #endif  // CONFIG_EXT_INTER
 
-#if CONFIG_OBMC
+#if CONFIG_MOTION_VAR
 /* returns subpixel variance error function */
 #define DIST(r, c) \
   vfp->osvf(pre(y, y_stride, r, c), y_stride, sp(c), sp(r), z, mask, &sse)
@@ -3414,4 +3414,4 @@ int av1_obmc_full_pixel_diamond(const AV1_COMP *cpi, MACROBLOCK *x,
   }
   return bestsme;
 }
-#endif  // CONFIG_OBMC
+#endif  // CONFIG_MOTION_VAR