ETM: more ETM_CTRL bit cleanup

ETM: more ETM_CTRL bit cleanup

Change handling of the CYCLE_ACCURATE, BRANCH_OUTPUT, and
TRACE_* flags; also the CONTEXTID size values.

 - Convert to symbols matching the actual register bits, instead of
   some random *other* bits (and then correcting that abuse).

 - Get rid of a now-needless enum.

 - Keep those values in etm->control, and remove etm->tracemode.

These values all affect the trace data that's recorded by a trace
pod or in the ETB.  I modified the file format used to dump ETB
data; since it's fairly clear nobody can use this mechanism now,
this can't cause anyone trouble.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>