Adding GSI public keys

This CL adds three GSI keys, to allow booting a GSI with AVB
to enable dm-verity.

   https://android.googlesource.com/platform/external/avb/

The keys for R and S GSI is to allow a device boots a new
version of GSI in a Treble-compatible manner.

For more information about GSI, please visit:

    https://source.android.com/setup/build/gsi

Bug: 112293933
Test: m q-gsi.avbpubkey r-gsi.avbpubkey s-gsi.avbpubkey
Change-Id: I4439e44fbd5da3240d7f6c7987f66445ec4590c5

rootdir/Android.mk

@@ -376,3 +376,5 @@ $(LOCAL_BUILT_MODULE):
 	$(hide) echo -n > $@
 	$(hide) $(foreach lib,$(PRIVATE_VNDK_SAMEPROCESS_LIBRARIES), \
 		echo $(lib).so >> $@;)
+
+include $(call all-makefiles-under,$(LOCAL_PATH))

rootdir/avb/Android.mk

@@ -0,0 +1,46 @@
+LOCAL_PATH:= $(call my-dir)
+
+#######################################
+# q-gsi.avbpubkey
+include $(CLEAR_VARS)
+
+LOCAL_MODULE := q-gsi.avbpubkey
+LOCAL_MODULE_CLASS := ETC
+LOCAL_SRC_FILES := $(LOCAL_MODULE)
+ifeq ($(BOARD_USES_RECOVERY_AS_BOOT),true)
+LOCAL_MODULE_PATH := $(TARGET_RECOVERY_ROOT_OUT)/first_stage_ramdisk/avb
+else
+LOCAL_MODULE_PATH := $(TARGET_RAMDISK_OUT)/avb
+endif
+
+include $(BUILD_PREBUILT)
+
+#######################################
+# r-gsi.avbpubkey
+include $(CLEAR_VARS)
+
+LOCAL_MODULE := r-gsi.avbpubkey
+LOCAL_MODULE_CLASS := ETC
+LOCAL_SRC_FILES := $(LOCAL_MODULE)
+ifeq ($(BOARD_USES_RECOVERY_AS_BOOT),true)
+LOCAL_MODULE_PATH := $(TARGET_RECOVERY_ROOT_OUT)/first_stage_ramdisk/avb
+else
+LOCAL_MODULE_PATH := $(TARGET_RAMDISK_OUT)/avb
+endif
+
+include $(BUILD_PREBUILT)
+
+#######################################
+# s-gsi.avbpubkey
+include $(CLEAR_VARS)
+
+LOCAL_MODULE := s-gsi.avbpubkey
+LOCAL_MODULE_CLASS := ETC
+LOCAL_SRC_FILES := $(LOCAL_MODULE)
+ifeq ($(BOARD_USES_RECOVERY_AS_BOOT),true)
+LOCAL_MODULE_PATH := $(TARGET_RECOVERY_ROOT_OUT)/first_stage_ramdisk/avb
+else
+LOCAL_MODULE_PATH := $(TARGET_RAMDISK_OUT)/avb
+endif
+
+include $(BUILD_PREBUILT)