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
diff --git a/fsgen/filesystem_creator.go b/fsgen/filesystem_creator.go
index 918e7d0..765b28f 100644
--- a/fsgen/filesystem_creator.go
+++ b/fsgen/filesystem_creator.go
@@ -757,6 +757,8 @@
 	}
 
 	fsProps.Is_auto_generated = proptools.BoolPtr(true)
+	// TODO(b/381120092): Verify mount_point for system partition
+	fsProps.Mount_point = proptools.StringPtr(partitionType)
 
 	partitionSpecificFsProps(ctx, fsProps, partitionVars, partitionType)