Start cleaning up ETM register handling. On one ARM926 ETM+ETB

Start cleaning up ETM register handling.  On one ARM926 ETM+ETB
system, removes 20 non-existent registers ... but still includes
over 45 (!) ETM registers which don't even exist there ...

 - Integrate the various tables to get one struct per register
 - Get rid of needless per-register dynamic allocation
 - Double check list of registers:
    * Remove sixteen (!) non-registers for data comparators
    * Remove four registers that imply newer ETM than we support
    * Change some names to match current architecture specs
 - Handle more register info
    * some are write-only
    * some are read-only
    * record which versions have them, just in case
 - Reorganize the registers to facilitate removing the extras
    * group e.g. comparator/counter #N registers together
    * add and use lookup-by-ID

git-svn-id: svn://svn.berlios.de/openocd/trunk@2751 b42882b7-edfa-0310-969c-e2dbd0fdcd60