Update default branch in .gitreview

Signed-off-by: Chris Brand <chris.brand@cypress.com>
Change-Id: I17d061668aad5af489f4f0d75ced92642a482ec7
diff --git a/.gitreview b/.gitreview
new file mode 100644
index 0000000..b0037ba
--- /dev/null
+++ b/.gitreview
@@ -0,0 +1,5 @@
+[gerrit]
+host=review.trustedfirmware.org
+port=29418
+project=TF-M/tf-m-extras
+defaultbranch=main