Cleanup and improve handle_wp_command and handle_rwp_command:

- Simplify argument parsing logic using switch statement.
- Use parse_u32 to ensure all values parse properly.
- Return syntax error when mode argument fails to parse.


git-svn-id: svn://svn.berlios.de/openocd/trunk@2236 b42882b7-edfa-0310-969c-e2dbd0fdcd60