refactor(amu): refactor enablement and context switching

This change represents a general refactoring to clean up old code that
has been adapted to account for changes required to enable dynamic
auxiliary counters.

Change-Id: Ia85e0518f3f65c765f07b34b67744fc869b9070d
Signed-off-by: Chris Kay <chris.kay@arm.com>
3 files changed