[TF-M] Deprecation of the nRF5340 PDK platform

Hello,

I would like to propose the deprecation of the nRF5340 PDK platform (nordic_nrf/nrf5340pdk_nrf5340_cpuapp) and the removal of this platform after the v1.3.0 release. The nRF5340 PDK is a preview development kit with an early revision (Engineering A) of the nRF5340 SoC and it has been replaced by the nRF5340 DK (as indicated here: https://www.nordicsemi.com/Software-and-tools/Development-Kits/nRF5340-PDK), which is also supported by TF-M. As per the process, should you have any objections to this deprecation, please respond to this proposal within 4 weeks.

Best regards, Andrzej Głąbek