Add build flags for spanning the super partition across multiple block devices.

This adds BOARD_SUPER_PARTITION_BLOCK_DEVICES, which must contain a list
of the (non-A/B suffixed) partitions that will comprise the super
partition. It is only intended for devices which cannot have a partition
named "super". For each entry, there must be a
BOARD_SUPER_PARTITION_x_DEVICE_SIZE variable defined with the exact size
of that partition (not its image size). The sum of these sizes must be
equal to BOARD_SUPER_PARTITION_SIZE.

Bug: 116802789
Test: device with BOARD_SUPER_PARTITION_BLOCK_DEVICES builds
Change-Id: I1a79c2e08ca99ce7e42207893ef3285caffecf44
diff --git a/core/main.mk b/core/main.mk
index 915d4be..7125fc5 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -250,6 +250,7 @@
 ADDITIONAL_PRODUCT_PROPERTIES += \
     ro.boot.logical_partitions=$(PRODUCT_USE_DYNAMIC_PARTITIONS) \
     ro.boot.dynamic_partitions=$(PRODUCT_USE_DYNAMIC_PARTITIONS) \
+    ro.boot.dynamic_partitions_retrofit=$(PRODUCT_RETROFIT_DYNAMIC_PARTITIONS)
 
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