Set grub timeout to zero

... to make the boot faster

Bug: 374848456
Test: check /boot/grub/grub.cfg and ensure timeout=0
Change-Id: Ie10870b2c66fcad20fbfd328647a475f641e0d97
diff --git a/build/debian/fai_config/files/etc/default/grub.d/15_timeout.cfg/AVF b/build/debian/fai_config/files/etc/default/grub.d/15_timeout.cfg/AVF
new file mode 100644
index 0000000..bc3e4d9
--- /dev/null
+++ b/build/debian/fai_config/files/etc/default/grub.d/15_timeout.cfg/AVF
@@ -0,0 +1 @@
+GRUB_TIMEOUT=0