util/release: Make signing with GPG 2 easier

GPG 2 expects the GPG_TTY variable to be configured so
that it can properly ask for the passphrase. If it's
not already set, do so.

Change-Id: I7e145a492c9eceda40cc1a1e04452a78852042d1
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36953
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/release/build-release

@@ -10,6 +10,10 @@ GPG_KEY_ID=$4
 
 set -e
 
+if [ -z "$GPG_TTY" ]; then
+	export GPG_TTY=$(tty)
+fi
+
 # set local + tz to be reproducible
 LC_ALL=C
 LANG=C