analysis/frequency: add per CPU frequency plotting
analysis/frequency: add per CPU frequency plotting

Using plotClusterFrequencies() is overkilling in some notebooks where we
need/want to focus on a specific CPU.

Teach the frequency_analysis how to generate plots for a list of specified
CPUs only.

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

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