[CFL] Move store flag to CFL_CTX

With recent changes, it is now possible to store the storage
flag inside the CFL_CTX. This simplifies the implementation
and will allow reuse in the decoder.

This change does not alter the bitstream.

Change-Id: Ibb8aebdd3d06f8765d40248ece8a038892e87032
diff --git a/av1/common/cfl.c b/av1/common/cfl.c
index a0ff45b..f0f6981 100644
--- a/av1/common/cfl.c
+++ b/av1/common/cfl.c
@@ -25,6 +25,7 @@
   cfl->subsampling_x = cm->subsampling_x;
   cfl->subsampling_y = cm->subsampling_y;
   cfl->are_parameters_computed = 0;
+  cfl->store_y = 0;
 }
 
 // Load from the CfL pixel buffer into output