objtool: Use "action" in error message to be consistent with help

The help message mentions the main options as "actions", which is
different from the optional "options". But the check error messages
outputs "option" or "command" for referring to actions.

Make the error messages consistent with help.

Signed-off-by: Siddh Raman Pant <siddh.raman.pant@oracle.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>