Derive kernel size from total and userspace sizes am: 13a164f1ba am: fd0a6f4043 am: de9dc0aacd

Original change: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/2362613

Change-Id: Ifd6424623b93d6b63df6d00ca7ae3ac8ba9bbc2e
Signed-off-by: Automerger Merge Worker <[email protected]>