[TF-M] Correction - MMIO region is not sharable between partitions

Hi,

In the tech forum I mentioned a potential way of sharing MMIO regions - this is not correct.

Double checked the PSA FF and it is defined explicitly in the spec page 43:

"A Secure Partition always has exclusive access to an MMIO region. Secure Partitions are not allowed to share MMIO regions with other Secure Partitions and MMIO regions are not allowed to overlap."

Sorry for the confusion.

BR

/Ken