rtc-screen: Increase the sad thresh for scroll detection

For the frame-level scroll detection on superblocks for
high motion content: increase the sad thresholds to avoid
mis-detection, and make it dependent on the motion magnitude.
This reduces the psnr dips in the issue below.

Bug: b:383306740
Change-Id: I0eb37de53285d6307b790cf3d8978e492d132ee0

av1/encoder/ratectrl.c

diff --git a/av1/encoder/ratectrl.c b/av1/encoder/ratectrl.c
index 5f3b206..2ff2a4e 100644
--- a/av1/encoder/ratectrl.c
+++ b/av1/encoder/ratectrl.c
@@ -3374,7 +3374,10 @@
                 cpi, src_y, last_src_y, src_ystride, last_src_ystride,
                 BLOCK_128X128, pos_col, pos_row, &best_intmv_col,
                 &best_intmv_row, sw_col, sw_row);
-            if (y_sad < 100 &&
+            unsigned int sad_thresh =
+                (abs(best_intmv_col) > 150 || abs(best_intmv_row) > 150) ? 300
+                                                                         : 150;
+            if (y_sad < sad_thresh &&
                 (abs(best_intmv_col) > 16 || abs(best_intmv_row) > 16)) {
               cpi->rc.high_motion_content_screen_rtc = 0;
               break;