Fixes to allow the ExecContext to be used for profiling.

Fixes to allow the ExecContext to be used for profiling.

cpu/base.cc:
    Change to be calls through the ExecContext instead of accessing the profile object directly.
cpu/cpu_exec_context.cc:
    Add functions to clear and sample the profile object.
cpu/cpu_exec_context.hh:
    Add functions to clear and sample the profile object.  These are not the most flexible functions; it might be better to eventually move the quiesce, profile, and store conditional stuff out of ExecContext so they don't clutter the interface.
cpu/exec_context.hh:
    Include functions to support using the profile object to clear itself and take samples.

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extra : convert_revision : 40849915fd51303673451515debb9ecdc7afb8c8