control: Create parameter trigger

Create a new event trigger that will run actions when a parameter is
either added, removed, or changed.

When the trigger is enabled it is added

control: Create parameter trigger

Create a new event trigger that will run actions when a parameter is
either added, removed, or changed.

When the trigger is enabled it is added to the Manager class since that
is where parameters are stored, and then the Manager watches for
parameter changes and runs actions as needed.

The JSON config would look like:
{
"class": "parameter",
"parameter": "pcie_floor_index"
}

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I8ff281d49ac780e8ff38f3e8ed02ab95395f1fd3

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