Add support to build system_dlkm.img

There are 2 choices to build system_dlkm.img for
the system_dlkm partition for Android T launch
devices and must choose one.

1. Use kernel prebuilt system_dlkm.img
   - BOARD_PREBUILT_SYSTEM_DLKM_IMAGE to point image
2. Build from kernel prebuilt system_dlkm_staging
   - PRODUCT_BUILD_SYSTEM_DLKM_IMAGE

Both requires: BOARD_SYSTEM_DLKM_PARTITION_SIZE and
must be 64MB or higher in size (enforced via vts).

Bug: 200082547
Test: TH
Test: atest vts_system_dlkm_partition_test
Signed-off-by: Ramji Jiyani <ramjiyani@google.com>
Change-Id: I83435123bd8aa3d04ab8a8b650a95fbab0bc49f2
diff --git a/core/config.mk b/core/config.mk
index 72b6ec8..6f22b7c 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -597,6 +597,7 @@
 FS_GET_STATS := $(HOST_OUT_EXECUTABLES)/fs_get_stats$(HOST_EXECUTABLE_SUFFIX)
 MKEXTUSERIMG := $(HOST_OUT_EXECUTABLES)/mkuserimg_mke2fs
 MKE2FS_CONF := system/extras/ext4_utils/mke2fs.conf
+MKEROFS := $(HOST_OUT_EXECUTABLES)/mkfs.erofs
 MKEROFSUSERIMG := $(HOST_OUT_EXECUTABLES)/mkerofsimage.sh
 MKSQUASHFSUSERIMG := $(HOST_OUT_EXECUTABLES)/mksquashfsimage.sh
 MKF2FSUSERIMG := $(HOST_OUT_EXECUTABLES)/mkf2fsuserimg.sh