libs/utils/env: make optional the test configuration
libs/utils/env: make optional the test configuration

It could be useful, on simple execution scenarios, to have just a target
configuration without any specific test configuration. This is not currenty
supported.

This patch makes the test configuration optional. Since even in simple
execution scenarios we are usually interested in using FTrace, this
option can now be configured also by the target configuration.
However, test configuration options always override target defined ones.

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

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