kho: simplify serialization and remove __kho_abort

Currently, __kho_finalize() performs memory serialization in the middle of
FDT construction. If FDT construction fails later, the function must
manually clean up the serialized memory via __kho_abort().

Refactor __kho_finalize() to perform kho_mem_serialize() only after the
FDT has been successfully constructed and finished. This reordering has
two benefits:
1. It avoids expensive serialization work if FDT generation fails.
2. It removes the need for cleanup in the FDT error path.

As a result, the internal helper __kho_abort() is no longer needed for
internal error handling. Inline its remaining logic (cleanup of the
preserved memory map) directly into kho_abort() and remove the helper.

Link: https://lkml.kernel.org/r/20251114190002.3311679-8-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baoquan He <bhe@redhat.com>
Cc: Coiby Xu <coxu@redhat.com>
Cc: Dave Vasilevsky <dave@vasilevsky.ca>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Kees Cook <kees@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>