libs/utils/trace: add support to register DataFrame getters
libs/utils/trace: add support to register DataFrame getters

A DataFrame getter is a method or attribute of a module which:
1) reference or point to a DataFrame
2) its name starts with "_dfg_" (short for DataFrameGetter)

This patch add the required support to populate a Trace::data_frame
attribute with references to DataFrame getters exposed by a module.

The new _registerDataFrameGetters() method is used to register SFG
exposed by the Trace module itself.

Signed-off-by: Patrick Bellasi <431c86f368affbc3148c4669fbd465131f7e82cb@arm.com>

joelagnel/lisa,bjackman/lisa,credp/lisa,arnoldlu/lisa,JaviMerino/lisa,credp/lisa,ARM-software/lisa,ARM-software/lisa,credp/lisa,credp/lisa,ARM-software/lisa,arnoldlu/lisa,mdigiorgio/lisa,ARM-software/lisa,bjackman/lisa,joelagnel/lisa,mdigiorgio/lisa