objtool: Allow stack operations in UNWIND_HINT_UNDEFINED regions

If the code specified UNWIND_HINT_UNDEFINED, skip the "undefined stack
state" warning due to a stack operation.  Just ignore the stack op and
continue to propagate the undefined state.

Link: https://lore.kernel.org/r/820c5b433f17c84e8761fb7465a8d319d706b1cf.1685981486.git.jpoimboe@kernel.org


Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>