enable LZ4 ramdisks for aosp_arm64

LZ4 is much faster to decompress than gzip.

Bug: 158791155
Change-Id: Id962c439c54e8c4fcca003acad3b7e09d1dec424
diff --git a/target/board/generic_arm64/BoardConfig.mk b/target/board/generic_arm64/BoardConfig.mk
index 0ac2f94..ba69623 100644
--- a/target/board/generic_arm64/BoardConfig.mk
+++ b/target/board/generic_arm64/BoardConfig.mk
@@ -64,6 +64,7 @@
 BOARD_KERNEL-5.4-LZ4_BOOTIMAGE_PARTITION_SIZE := 53477376
 BOARD_USERDATAIMAGE_PARTITION_SIZE := 576716800
 
+BOARD_RAMDISK_USE_LZ4 := true
 BOARD_BOOT_HEADER_VERSION := 3
 BOARD_MKBOOTIMG_ARGS += --header_version $(BOARD_BOOT_HEADER_VERSION)