Add a q index based frame superres mode

Refactors and adds superres-mode 3 and associated
paramters --superres-qthresh and --superres-kf-qthresh
that are used to trigger superres mode when the qindex
for any frame exceeds the thresholds provided for non-key
and key-frames respenctively. The superres scale factor
numerator is progressively reduced from 16 starting from
that q threshold following a fixed slope.

Change-Id: If1c782993667a6fbaaa01bbde77c4924008c0d28

av1/common/alloccommon.c

diff --git a/av1/common/alloccommon.c b/av1/common/alloccommon.c
index c878939..357543e 100644
--- a/av1/common/alloccommon.c
+++ b/av1/common/alloccommon.c
@@ -19,6 +19,22 @@
 #include "av1/common/entropymv.h"
 #include "av1/common/onyxc_int.h"
 
+int av1_get_MBs(int width, int height) {
+  const int aligned_width = ALIGN_POWER_OF_TWO(width, 3);
+  const int aligned_height = ALIGN_POWER_OF_TWO(height, 3);
+  const int mi_cols = aligned_width >> MI_SIZE_LOG2;
+  const int mi_rows = aligned_height >> MI_SIZE_LOG2;
+
+#if CONFIG_CB4X4
+  const int mb_cols = (mi_cols + 2) >> 2;
+  const int mb_rows = (mi_rows + 2) >> 2;
+#else
+  const int mb_cols = (mi_cols + 1) >> 1;
+  const int mb_rows = (mi_rows + 1) >> 1;
+#endif
+  return mb_rows * mb_cols;
+}
+
 void av1_set_mb_mi(AV1_COMMON *cm, int width, int height) {
   // Ensure that the decoded width and height are both multiples of
   // 8 luma pixels (note: this may only be a multiple of 4 chroma pixels if