Specify `mount_point` in autogenerated partitions

If unspecified, this defaults to `/`. Specifying the mount point is
necessary for creating bit-identical make and soong img files.

Bug: 383357338
Test: lunch aosp_cf_x86_64_phone-trunk_staging-userdebug
Setup
- export COPY_IMAGES_FOR_TARGET_FILES_ZIP=true
- export BUILD_DATETIME=10
- commented out installed_*_notice_xml_gz in build/make/core/Makefile
Test: verified that the following .img files are bit identical in top of
CL stack
odm,system_dlkm,vendor_dlkm,odm_dlkm

Change-Id: Ie620e4f99d95d2391e7ac0f8d48b54e8d754c9f9