FP5: Freeze AVB rollback index

This should provide better compatibility with stock OS and third party
ROMs that have proper AVB setup with relocked bootloader.

Change-Id: I8a30eea8a766b0a7b6d71cfdd4cf82d506c89426
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 540d517..388f9f1 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -167,13 +167,14 @@
 BOARD_VENDOR_SEPOLICY_DIRS += $(DEVICE_PATH)/sepolicy/vendor
 
 # Verified Boot
+STOCK_SECURITY_PATCH := 2024-04-05 # Latest stock update available
 BOARD_AVB_ENABLE := true
 BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --flags 3
 BOARD_AVB_ALGORITHM := SHA256_RSA4096
 BOARD_AVB_VBMETA_SYSTEM := system system_ext product
 BOARD_AVB_VBMETA_SYSTEM_ALGORITHM := SHA256_RSA4096
 BOARD_AVB_VBMETA_SYSTEM_KEY_PATH := external/avb/test/data/testkey_rsa4096.pem
-BOARD_AVB_VBMETA_SYSTEM_ROLLBACK_INDEX := $(PLATFORM_SECURITY_PATCH_TIMESTAMP)
+BOARD_AVB_VBMETA_SYSTEM_ROLLBACK_INDEX := $(shell date -d 'TZ="GMT" $(STOCK_SECURITY_PATCH)' +%s)
 BOARD_AVB_VBMETA_SYSTEM_ROLLBACK_INDEX_LOCATION := 2
 
 # Wifi