[TF-A] MTE support at S-EL1

Hi,

I've started to experiment with MTE in OP-TEE at S-EL1. I've compiled TF-A with CTX_INCLUDE_MTE_REGS and I'm testing this on QEMU. Before trying to use MTE in OP-TEE I check id_aa64pfr1_el1 and skip MTE initializations if unavailable.

This works as long as TF-A always is compiled with CTX_INCLUDE_MTE_REGS if MTE is available. If TF-A is compiled without CTX_INCLUDE_MTE_REGS OP-TEE will be trapped into EL3 when trying to access one of the MTE registers. I suppose this is because SCR_EL3.ATA is 0. Is there a way for OP-TEE to tell if the MTE registers are safe to access?

Thanks, Jens