interface: arm_ffa: Add FFA_YIELD SMC opcode am: bab99ee7cf

Original change: https://android-review.googlesource.com/c/trusty/lib/+/3464479

Change-Id: Ibabc7c7843b414376dab57fe05e9e495064e7335
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>