chore: add encrypt_fw to gitignore

Add tools/encrypt_fw/encrypt_fw & tools/encrypt_fw/encrypt_fw.exe to
.gitignore file, to avoid git listing those binary files.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I2f4ddbe1c11848513fe20f7c8b448a041988cc4f
diff --git a/.gitignore b/.gitignore
index 1f4efb6..ab2c0c4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,6 +31,8 @@
 tools/stm32image/stm32image
 tools/stm32image/stm32image.exe
 tools/sptool/__pycache__/
+tools/encrypt_fw/encrypt_fw
+tools/encrypt_fw/encrypt_fw.exe
 
 # GNU GLOBAL files
 GPATH