Avoid using sender/receiver from SPCI_MSG_SEND in memory sharing tests.

Instead we can use hf_vm_get_id() and memory_region->sender. This will
make it simpler when we remove our legacy 'architected messages' for
memory sharing.

Bug: 132420445
Change-Id: I5121b610d0dae1a08bba732f96ebc9b8e4e16468
1 file changed