tools: Improve PSA target identification logic
tools: Improve PSA target identification logic

Current logic `is_TFM_target` relies on the availability of attribute
`tfm_target_name` to identify PSA targets. The API `is_TFM_target` is
used in pytest to validate PSA target configuration which again checks
the availability of `tfm_target_name`. If a target doesn't contain the
attribute `tfm_target_name` then this check will fail instead of
catching it. Therefore, we now check for `TFM` config option in `labels`
attribute.

The API `is_TFM_target()` returns true for Mbed OS PSA targets which are
supported by TF-M also.

Add a new API `is_PSA_target()` which returns true for all Mbed OS PSA
targets.

Signed-off-by: Devaraj Ranganna <53e2fcb007e5c6e2caf46b91114119a655266f64@arm.com>

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