[TF-M] Deprecation of ARM/MPS2/fvp_sse300 platform

Hi Everyone,

I would like to propose the deprecation of arm/mps2/fvp_sse300 platform because the main platform for Corstone-300 is MPS3, available in arm/mps3/an547 and we would like to reduce the number of the platforms to maintain. Following the deprecation process, https://tf-m-user-guide.trustedfirmware.org/platform/ext/platform_deprecatio... this proposal is open for discussion at least for 4 weeks before the platform will be marked as deprecated and removed from TF-M unless any objection received.

Thanks and Best regards, Anton Komlev