GSI: adds /odm mount point in root dir

Bug: 64700195
Test: boot A/B device with /odm
Change-Id: Ie014a052a333b2cb8d89bc43e4326be81e638dcd
diff --git a/target/board/generic_arm64_ab/BoardConfig.mk b/target/board/generic_arm64_ab/BoardConfig.mk
index 56cc2da..1cab844 100644
--- a/target/board/generic_arm64_ab/BoardConfig.mk
+++ b/target/board/generic_arm64_ab/BoardConfig.mk
@@ -34,7 +34,7 @@
 BOARD_BUILD_SYSTEM_ROOT_IMAGE := true
 
 # TODO(jiyong) These might be SoC specific.
-BOARD_ROOT_EXTRA_FOLDERS := bt_firmware firmware firmware/radio persist
+BOARD_ROOT_EXTRA_FOLDERS += bt_firmware firmware firmware/radio persist
 BOARD_ROOT_EXTRA_SYMLINKS := /vendor/lib/dsp:/dsp
 
 # TODO(b/36764215): remove this setting when the generic system image
diff --git a/target/board/treble_common.mk b/target/board/treble_common.mk
index f7c8b32..8637235 100644
--- a/target/board/treble_common.mk
+++ b/target/board/treble_common.mk
@@ -56,3 +56,8 @@
 # TODO(b/35790399): remove when b/35790399 is fixed.
 BOARD_NAND_SPARE_SIZE := 0
 BOARD_FLASH_BLOCK_SIZE := 512
+
+# b/64700195: add minimum support for odm.img
+# Currently odm.img can only be built by `make custom_images`.
+# Adding /odm mount point under root directory.
+BOARD_ROOT_EXTRA_FOLDERS += odm