UPSTREAM: Documentation/kbuild: Add new gendwarfksyms kABI rules

Document the "byte_size" and "type_string" kABI stability rules.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
(cherry picked from commit cf9d6926)

Bug: 400972353
Link: https://lore.kernel.org/lkml/20250507231403.377725-12-samitolvanen@google.com/


Change-Id: I5add32d539103cdc0ec723efc424b800fb55f53d
Signed-off-by: Giuliano Procida <gprocida@google.com>
[jstultz: Switched to UPSTREAM]
Signed-off-by: John Stultz <jstultz@google.com>