[python] add `pyfinite` module to requirements

The `pyfinite` module is required to implement flash image scrambling,
required to backdoor load flash images in DV when scrambling is enabled.

Signed-off-by: Timothy Trippel <ttrippel@google.com>
diff --git a/python-requirements.txt b/python-requirements.txt
index 991fa5a..700f56d 100644
--- a/python-requirements.txt
+++ b/python-requirements.txt
@@ -17,6 +17,9 @@
 tabulate==0.8.10
 typer==0.6.1
 
+# Dependencies: gen-flash-img.py
+pyfinite==1.9.1
+
 # Dependencies: dv_sim
 enlighten==1.10.2
 mistletoe==0.9.0