Remove pointer from MB_MODE_INFO_EXT

MB_MODE_INFO_EXT contains pointer to tcoeff,eobs,
txb_skip_ctx and dc_sign_ctx which can be calculated
on the fly

Observed memory footprint reduction with no impact on
encoder performance.

stream                   cpu-used  encoder
BasketballDrill_832x480     1      ~1.42%
parkrun_720p50              3      ~1.32%

Change-Id: I47b4a9773bb62995b93be4a503975d16b2af0607
diff --git a/av1/encoder/block.h b/av1/encoder/block.h
index 331c4a0..96b0991 100644
--- a/av1/encoder/block.h
+++ b/av1/encoder/block.h
@@ -75,12 +75,10 @@
 
 typedef struct {
   // TODO(angiebird): Reduce the buffer size according to sb_type
-  tran_low_t *tcoeff[MAX_MB_PLANE];
-  uint16_t *eobs[MAX_MB_PLANE];
-  uint8_t *txb_skip_ctx[MAX_MB_PLANE];
-  int *dc_sign_ctx[MAX_MB_PLANE];
+  CB_COEFF_BUFFER *cb_coef_buff;
   CANDIDATE_MV ref_mv_stack[MODE_CTX_REF_FRAMES][MAX_REF_MV_STACK_SIZE];
   int_mv global_mvs[REF_FRAMES];
+  int cb_offset;
   int16_t mode_context[MODE_CTX_REF_FRAMES];
   uint8_t ref_mv_count[MODE_CTX_REF_FRAMES];
 } MB_MODE_INFO_EXT;