ppc sim: Improve invalid option error message

ppc sim: Improve invalid option error message

This patch improves the error message when an invalid option is
detected, by also printing the option that actually caused the error.
For instance, from GDB:

        (gdb) target sim --hello
        Invalid option: --hello
        Usage:
        [...]

We also added the usage after an invalid long-name option (Eg: --hello)
to be in line with what's being done for all other invalid options
being detected.

sim/ppc/ChangeLog:

        * psim.c (psim_options): Add option that cause the error
        in invalid-option error messages. Print the usage when
        detecting an invalid long-name option.