Allows skipping building the super images for partial builds.

Previously, setting PRODUCT_BUILD_SUPER_PARTITION to false for a partial
build (with PRODUCT_USE_DYNAMIC_PARTITIONS == true) would fail to
include necessary keys in misc_info.txt that are required when merging
two partial builds to create a dynamic-partition-enabled mixed build.

This change ensures these necessary keys are included even when
PRODUCT_BUILD_SUPER_PARTITION is false. Setting
PRODUCT_BUILD_SUPER_PARTITION to false causes partial builds to skip
building super.img and super_empty.img, instead relying on these images
to come from the final merged build.

Bug: 134764140
Test: Building & booting a dynamic-partition-enabled mixed build, and
inspecting partial builds' logs / out folder to ensure that
super.img/super_empty.img were not created.

Change-Id: I99431a9a342e9b0617510e250597f3024ef39322