Set BOOT_SECURITY_PATCH

* This is put in vbmeta, and Fairphone OS sets it

Change-Id: I69485c8207eca5ee9e7f1f4e02d684707c6dece3
diff --git a/BoardConfig.mk b/BoardConfig.mk
index ca81a14..2e1fb2d 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -190,6 +190,7 @@
 ENABLE_VENDOR_RIL_SERVICE := true
 
 # Security patch level
+BOOT_SECURITY_PATCH := 2022-08-05
 VENDOR_SECURITY_PATCH := 2022-08-05
 
 # SEPolicy